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Low framerate with dma-buf output #35

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Ordspilleren opened this issue Apr 26, 2018 · 31 comments
Closed

Low framerate with dma-buf output #35

Ordspilleren opened this issue Apr 26, 2018 · 31 comments

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@Ordspilleren
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@Ordspilleren Ordspilleren commented Apr 26, 2018

Hello,

I have dma-buf working with GVT-g on kernel 4.16 and QEMU 2.12. The framerate of the framebuffer output is very low however (seems to be around ~20 fps). I've run the Heaven benchmark in the VM, and that seems to perform about as expected, so it's only the dma-buf output that's slow. Does anyone else experience this?

I'm using Libvirt with local SPICE and OpenGL. Also tried different Intel drivers in the VM, no difference.

@Saren-Arterius
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@Saren-Arterius Saren-Arterius commented May 5, 2018

Same here. What can be changed to improve the framerate?

zhenyw pushed a commit that referenced this issue May 16, 2018
syzbot caught an infinite recursion in nsh_gso_segment().

Problem here is that we need to make sure the NSH header is of
reasonable length.

BUG: MAX_LOCK_DEPTH too low!
turning off the locking correctness validator.
depth: 48  max: 48!
48 locks held by syz-executor0/10189:
 #0:         (ptrval) (rcu_read_lock_bh){....}, at: __dev_queue_xmit+0x30f/0x34c0 net/core/dev.c:3517
 #1:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #1:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #2:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #2:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #3:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #3:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #4:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #4:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #5:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #5:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #6:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #6:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #7:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #7:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #8:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #8:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #9:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #9:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #10:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #10:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #11:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #11:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #12:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #12:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #13:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #13:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #14:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #14:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #15:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #15:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #16:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #16:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #17:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #17:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #18:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #18:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #19:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #19:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #20:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #20:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #21:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #21:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #22:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #22:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #23:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #23:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #24:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #24:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #25:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #25:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #26:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #26:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #27:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #27:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #28:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #28:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #29:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #29:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #30:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #30:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #31:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #31:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
dccp_close: ABORT with 65423 bytes unread
 #32:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #32:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #33:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #33:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #34:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #34:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #35:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #35:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #36:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #36:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #37:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #37:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #38:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #38:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #39:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #39:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #40:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #40:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #41:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #41:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #42:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #42:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #43:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #43:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #44:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #44:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #45:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #45:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #46:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #46:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
 #47:         (ptrval) (rcu_read_lock){....}, at: __skb_pull include/linux/skbuff.h:2080 [inline]
 #47:         (ptrval) (rcu_read_lock){....}, at: skb_mac_gso_segment+0x221/0x720 net/core/dev.c:2787
INFO: lockdep is turned off.
CPU: 1 PID: 10189 Comm: syz-executor0 Not tainted 4.17.0-rc2+ #26
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b9/0x294 lib/dump_stack.c:113
 __lock_acquire+0x1788/0x5140 kernel/locking/lockdep.c:3449
 lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
 rcu_lock_acquire include/linux/rcupdate.h:246 [inline]
 rcu_read_lock include/linux/rcupdate.h:632 [inline]
 skb_mac_gso_segment+0x25b/0x720 net/core/dev.c:2789
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 nsh_gso_segment+0x405/0xb60 net/nsh/nsh.c:107
 skb_mac_gso_segment+0x3ad/0x720 net/core/dev.c:2792
 __skb_gso_segment+0x3bb/0x870 net/core/dev.c:2865
 skb_gso_segment include/linux/netdevice.h:4025 [inline]
 validate_xmit_skb+0x54d/0xd90 net/core/dev.c:3118
 validate_xmit_skb_list+0xbf/0x120 net/core/dev.c:3168
 sch_direct_xmit+0x354/0x11e0 net/sched/sch_generic.c:312
 qdisc_restart net/sched/sch_generic.c:399 [inline]
 __qdisc_run+0x741/0x1af0 net/sched/sch_generic.c:410
 __dev_xmit_skb net/core/dev.c:3243 [inline]
 __dev_queue_xmit+0x28ea/0x34c0 net/core/dev.c:3551
 dev_queue_xmit+0x17/0x20 net/core/dev.c:3616
 packet_snd net/packet/af_packet.c:2951 [inline]
 packet_sendmsg+0x40f8/0x6070 net/packet/af_packet.c:2976
 sock_sendmsg_nosec net/socket.c:629 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:639
 __sys_sendto+0x3d7/0x670 net/socket.c:1789
 __do_sys_sendto net/socket.c:1801 [inline]
 __se_sys_sendto net/socket.c:1797 [inline]
 __x64_sys_sendto+0xe1/0x1a0 net/socket.c:1797
 do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Fixes: c411ed8 ("nsh: add GSO support")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jiri Benc <jbenc@redhat.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Acked-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
@bangom
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@bangom bangom commented Aug 5, 2018

Same here, refresh rate of whole "dmabuffed" display is really bad via Spice or GTK. OpenGL / DirectX apps FPS seems OK. Tested on Windows 10 Enterprise 1803 Guest with latest 24.20.100.6194 Intel drivers, custom compiled Qemu 2.12.1 and 4.18.0 kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline/drm-intel-nightly/2018-08-03/ (using it because of another bug)... all on Ubuntu 18.04. Any help please?

@bangom
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@bangom bangom commented Aug 11, 2018

When using spicy client conneced to local dmabuff VM try turning off spice protocol compression, refreshrate seems normal OK then!

qemu-system-x86_64 ... -spice disable-ticketing,port=5910,image-compression=off,streaming-video=off,playback-compression=off,jpeg-wan-compression=never,zlib-glz-wan-compression=never

@worron
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@worron worron commented Aug 15, 2018

@bangom
Do you managed to get real 60fps with spice? I tried dma-buf with spice no compression and gtk but fps always about 20-30 (visually) despite inner counters in games and benchmarks shows much more.

@bangom
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@bangom bangom commented Aug 15, 2018

@worron, well maybe not 60fps... more like 30fps. But huge step when comparing spice compression on (~5fps) and off (~30fps). Hope there will be fix soon so we can use GVT in OpenGL game scenarios on a Windows host.

@worron
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@worron worron commented Aug 15, 2018

OK, thanks for clarification. Current state of dma-buf (~30fps) is pretty good but still not perfect. I'm just following the issue hoping for improvements.

@Saren-Arterius
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@Saren-Arterius Saren-Arterius commented Aug 18, 2018

Tried gnif/looking-glass on a win10, can achieve 60fps in testufo, when under some kind of GPU load the fps drops to 10ish, not better than dma-buf for this case.

@Saren-Arterius
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@Saren-Arterius Saren-Arterius commented Aug 18, 2018

When under heavy load (3dmark) dma-buf stutters really bad, it could freeze for 0.5s before showing next frame, while the 3dmark runs at 12-15fp

Using virt-manager, gpu is uhd620

@zhangchn
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@zhangchn zhangchn commented Nov 13, 2018

Hi, DMA-Buf via GTK is throttled to 33Hz by default fresh rate of GTK display.

Change definition of macro GUI_REFRESH_INTERVAL_DEFAULT in include/ui/console.h to 16 or 17 (milliseconds) and then rebuild qemu.

I have filed a bug at launchpad.net for qemu.

@Saren-Arterius
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@Saren-Arterius Saren-Arterius commented Nov 13, 2018

@zhangchn
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@zhangchn zhangchn commented Nov 13, 2018

Thanks! I wonder why is the throttle 33hz, instead of 60hz or client display refresh rate.

Tracking down the commit history, the interval of 30 milliseconds dates back to 10+ years ago when VGA emulation was first introduced.

qemu/qemu@313aa56

@worron
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@worron worron commented Nov 16, 2018

@zhangchn, thank you! Finally can enjoy fair 60fps in gvt accelerated VM.

Also I'm asking all concerned to vote the bug at launchpad.

zhenyw pushed a commit that referenced this issue Nov 19, 2018
Increase kasan instrumented kernel stack size from 32k to 64k. Other
architectures seems to get away with just doubling kernel stack size under
kasan, but on s390 this appears to be not enough due to bigger frame size.
The particular pain point is kasan inlined checks (CONFIG_KASAN_INLINE
vs CONFIG_KASAN_OUTLINE). With inlined checks one particular case hitting
stack overflow is fs sync on xfs filesystem:

 #0 [9a0681e8]  704 bytes  check_usage at 34b1fc
 #1 [9a0684a8]  432 bytes  check_usage at 34c710
 #2 [9a068658]  1048 bytes  validate_chain at 35044a
 #3 [9a068a70]  312 bytes  __lock_acquire at 3559fe
 #4 [9a068ba8]  440 bytes  lock_acquire at 3576ee
 #5 [9a068d60]  104 bytes  _raw_spin_lock at 21b44e0
 #6 [9a068dc8]  1992 bytes  enqueue_entity at 2dbf72
 #7 [9a069590]  1496 bytes  enqueue_task_fair at 2df5f0
 #8 [9a069b68]  64 bytes  ttwu_do_activate at 28f438
 #9 [9a069ba8]  552 bytes  try_to_wake_up at 298c4c
 #10 [9a069dd0]  168 bytes  wake_up_worker at 23f97c
 #11 [9a069e78]  200 bytes  insert_work at 23fc2e
 #12 [9a069f40]  648 bytes  __queue_work at 2487c0
 #13 [9a06a1c8]  200 bytes  __queue_delayed_work at 24db28
 #14 [9a06a290]  248 bytes  mod_delayed_work_on at 24de84
 #15 [9a06a388]  24 bytes  kblockd_mod_delayed_work_on at 153e2a0
 #16 [9a06a3a0]  288 bytes  __blk_mq_delay_run_hw_queue at 158168c
 #17 [9a06a4c0]  192 bytes  blk_mq_run_hw_queue at 1581a3c
 #18 [9a06a580]  184 bytes  blk_mq_sched_insert_requests at 15a2192
 #19 [9a06a638]  1024 bytes  blk_mq_flush_plug_list at 1590f3a
 #20 [9a06aa38]  704 bytes  blk_flush_plug_list at 1555028
 #21 [9a06acf8]  320 bytes  schedule at 219e476
 #22 [9a06ae38]  760 bytes  schedule_timeout at 21b0aac
 #23 [9a06b130]  408 bytes  wait_for_common at 21a1706
 #24 [9a06b2c8]  360 bytes  xfs_buf_iowait at fa1540
 #25 [9a06b430]  256 bytes  __xfs_buf_submit at fadae6
 #26 [9a06b530]  264 bytes  xfs_buf_read_map at fae3f6
 #27 [9a06b638]  656 bytes  xfs_trans_read_buf_map at 10ac9a8
 #28 [9a06b8c8]  304 bytes  xfs_btree_kill_root at e72426
 #29 [9a06b9f8]  288 bytes  xfs_btree_lookup_get_block at e7bc5e
 #30 [9a06bb18]  624 bytes  xfs_btree_lookup at e7e1a6
 #31 [9a06bd88]  2664 bytes  xfs_alloc_ag_vextent_near at dfa070
 #32 [9a06c7f0]  144 bytes  xfs_alloc_ag_vextent at dff3ca
 #33 [9a06c880]  1128 bytes  xfs_alloc_vextent at e05fce
 #34 [9a06cce8]  584 bytes  xfs_bmap_btalloc at e58342
 #35 [9a06cf30]  1336 bytes  xfs_bmapi_write at e618de
 #36 [9a06d468]  776 bytes  xfs_iomap_write_allocate at ff678e
 #37 [9a06d770]  720 bytes  xfs_map_blocks at f82af8
 #38 [9a06da40]  928 bytes  xfs_writepage_map at f83cd6
 #39 [9a06dde0]  320 bytes  xfs_do_writepage at f85872
 #40 [9a06df20]  1320 bytes  write_cache_pages at 73dfe8
 #41 [9a06e448]  208 bytes  xfs_vm_writepages at f7f892
 #42 [9a06e518]  88 bytes  do_writepages at 73fe6a
 #43 [9a06e570]  872 bytes  __writeback_single_inode at a20cb6
 #44 [9a06e8d8]  664 bytes  writeback_sb_inodes at a23be2
 #45 [9a06eb70]  296 bytes  __writeback_inodes_wb at a242e0
 #46 [9a06ec98]  928 bytes  wb_writeback at a2500e
 #47 [9a06f038]  848 bytes  wb_do_writeback at a260ae
 #48 [9a06f388]  536 bytes  wb_workfn at a28228
 #49 [9a06f5a0]  1088 bytes  process_one_work at 24a234
 #50 [9a06f9e0]  1120 bytes  worker_thread at 24ba26
 #51 [9a06fe40]  104 bytes  kthread at 26545a
 #52 [9a06fea8]             kernel_thread_starter at 21b6b62

To be able to increase the stack size to 64k reuse LLILL instruction
in __switch_to function to load 64k - STACK_FRAME_OVERHEAD - __PT_SIZE
(65192) value as unsigned.

Reported-by: Benjamin Block <bblock@linux.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
@CuriousTommy
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@CuriousTommy CuriousTommy commented Dec 15, 2018

Here is a link to the launchpad report: https://bugs.launchpad.net/qemu/+bug/1802915

@CuriousTommy
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@CuriousTommy CuriousTommy commented Feb 14, 2019

@zhangchn I was wondering, is there a formula that determines what the GUI_REFRESH_INTERVAL is (How did you know to use 16 or 17 milliseconds to get 60hz)?

Someone could make a function that sets the right value based on the monitor that is currently connected.

@mafrasi2
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@mafrasi2 mafrasi2 commented Mar 8, 2019

@CuriousTommy That's just the inverse of 60hz: 1/60hz=0.016666s.

@Saren-Arterius
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@Saren-Arterius Saren-Arterius commented Mar 25, 2019

https://gist.github.com/Saren-Arterius/b31df23d5c359523f1ef430d27b0e834
Here is my 2 revisions of qemu patch attempt. They should fail miserably.

@ChristophSchmidpeter
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@ChristophSchmidpeter ChristophSchmidpeter commented Mar 5, 2020

Hi, DMA-Buf via GTK is throttled to 33Hz by default fresh rate of GTK display.

Change definition of macro GUI_REFRESH_INTERVAL_DEFAULT in include/ui/console.h to 16 or 17 (milliseconds) and then rebuild qemu.

I have filed a bug at launchpad.net for qemu.

I have set GUI_REFRESH_INTERVAL_DEFAULT to 17 as described and then recompiled quemu, but the framerate seems to bee still as low as before. Does anyone have the same issue, or know why that might be?

@ChristophSchmidpeter
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@ChristophSchmidpeter ChristophSchmidpeter commented Mar 5, 2020

@TerrenceXu : Is there any plan to implement adaptive fps in the near future? I think that would be very important for gvt to be more practical/useful.

@SanderVocke
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@SanderVocke SanderVocke commented Apr 24, 2020

@TitusLabienus: I just upgraded from qemu 4.2.0 (the Arch repository package) to qemu 5.0.0 rc4 (the Arch AUR qemu-git package), which I have modified with GUI_REFRESH_INTERVAL_DEFAULT=17.

I noticed a definite improvement in smoothness. In the guest I opened a YouTube video with a 30fps/60fps side-by-side comparison and could clearly see that the 60fps was way smoother.

However, the mouse cursor is still very choppy and still "feels" like 30fps, which is surprising to me.

Does anyone know if there is something special going on with the mouse in qemu with Intel GVT-g?

@j1warren
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@j1warren j1warren commented Jun 21, 2020

Relevant patch

@metenn
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@metenn metenn commented Jun 22, 2020

I have set GUI_REFRESH_INTERVAL_DEFAULT to 17 as described and then recompiled quemu, but the framerate seems to bee still as low as before. Does anyone have the same issue, or know why that might be?

Are you 100% sure that Qemu is using the newly compiled binaries? I was stupid enough to just run make install thinking that'd do it, but virt-manager was running qemu from /usr/bin, and make install only moved it to /usr/local/bin.

Relevant patch

Was this not merged to the master branch already?
https://github.com/qemu/qemu/blob/master/ui/gtk.c#L2038
Relevant commits
qemu/qemu@c4c0092
qemu/qemu@31ab416
qemu/qemu@7f4d96f

Am I the only one still struggling with a laggy/stuttery/"30FPS" mouse in the libvirt viewer, even after applying the "60FPS" patch?

@UmashankarTriforce
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@UmashankarTriforce UmashankarTriforce commented Jun 23, 2020

@matthiasmeten Nope you're not the only one. I'm stuck with Low FPS mouse cursor with 60FPS virtualized desktop. Any fix for this?

@metenn
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@metenn metenn commented Jun 23, 2020

Passing through a mouse, for instance, makes it smooth, but now I notice some general visual latency. Could be my video mode though

@UmashankarTriforce
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@UmashankarTriforce UmashankarTriforce commented Jun 24, 2020

I'm working this out on my laptop and I have passed through my touchpad to guest using evdev tutorial I found online. The cursor lag seems to disappear when I remove spice channel from my vm but the rendered resolution is wrong (though the guest reports 1920x1080, the display window has vertical bars on the side). If I add spice channel back, the mouse cursor starts lagging. Is this something related to spice buffers?

Edit: Fixed it by adding xres and yres Refer

@nikp123
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@nikp123 nikp123 commented Aug 17, 2020

@metenn @UmashankarTriforce Am the dev who send the initial patch here. I've tracked down the bug, but the repair requires input from the guys maintaining that piece of code, I've already tried to email kraxel, but I got no reply.

The issue is that the check ALWAYS fails due to an oversight in the "execution procedure". At the time when gd_refresh_rate_millihz gets executed, neither s->window or vc->window can be used. This is because vc->window has not been initialized, while s->window is hidden, thus failing the check if(win).

So this means that the code is effectively (so called 'ghost code') that never gets executed.

When does the function run exactly? Only during window initialization.

@nikp123
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@nikp123 nikp123 commented Aug 17, 2020

I've got two, somewhat sane solutions, but obviously I need input, since I'm not too familiar with the QEMU codebase.

  1. Move the check somewhere else, like a window resize (if possible)
  2. Yank that window open for just a brief moment so the pointer is valid (kinda hacky and will need some justification for it's existence)
@nikp123
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@nikp123 nikp123 commented Aug 17, 2020

And no, removing the check doesn't work, since it will always default to monitor 0, which might not be the one you're using fxp.

@nikp123
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@nikp123 nikp123 commented Aug 17, 2020

@kraxel Hate to bother you, but can you give your input on this, I would greatly appreciate it. Thanks for your work, by the way.

@nikp123
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@nikp123 nikp123 commented Aug 17, 2020

Nevermind, one of the maintainers got to me and wrote a patch. Should be merged pretty quick.

zhiwang1 pushed a commit that referenced this issue Sep 2, 2020
In the existing NVMeOF Passthru core command handling on failure of
nvme_alloc_request() it errors out with rq value set to NULL. In the
error handling path it calls blk_put_request() without checking if
rq is set to NULL or not which produces following Oops:-

[ 1457.346861] BUG: kernel NULL pointer dereference, address: 0000000000000000
[ 1457.347838] #PF: supervisor read access in kernel mode
[ 1457.348464] #PF: error_code(0x0000) - not-present page
[ 1457.349085] PGD 0 P4D 0
[ 1457.349402] Oops: 0000 [#1] SMP NOPTI
[ 1457.349851] CPU: 18 PID: 10782 Comm: kworker/18:2 Tainted: G           OE     5.8.0-rc4nvme-5.9+ #35
[ 1457.350951] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e3214
[ 1457.352347] Workqueue: events nvme_loop_execute_work [nvme_loop]
[ 1457.353062] RIP: 0010:blk_mq_free_request+0xe/0x110
[ 1457.353651] Code: 3f ff ff ff 83 f8 01 75 0d 4c 89 e7 e8 1b db ff ff e9 2d ff ff ff 0f 0b eb ef 66 8
[ 1457.355975] RSP: 0018:ffffc900035b7de0 EFLAGS: 00010282
[ 1457.356636] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000002
[ 1457.357526] RDX: ffffffffa060bd05 RSI: 0000000000000000 RDI: 0000000000000000
[ 1457.358416] RBP: 0000000000000037 R08: 0000000000000000 R09: 0000000000000000
[ 1457.359317] R10: 0000000000000000 R11: 000000000000006d R12: 0000000000000000
[ 1457.360424] R13: ffff8887ffa68600 R14: 0000000000000000 R15: ffff8888150564c8
[ 1457.361322] FS:  0000000000000000(0000) GS:ffff888814600000(0000) knlGS:0000000000000000
[ 1457.362337] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1457.363058] CR2: 0000000000000000 CR3: 000000081c0ac000 CR4: 00000000003406e0
[ 1457.363973] Call Trace:
[ 1457.364296]  nvmet_passthru_execute_cmd+0x150/0x2c0 [nvmet]
[ 1457.364990]  process_one_work+0x24e/0x5a0
[ 1457.365493]  ? __schedule+0x353/0x840
[ 1457.365957]  worker_thread+0x3c/0x380
[ 1457.366426]  ? process_one_work+0x5a0/0x5a0
[ 1457.366948]  kthread+0x135/0x150
[ 1457.367362]  ? kthread_create_on_node+0x60/0x60
[ 1457.367934]  ret_from_fork+0x22/0x30
[ 1457.368388] Modules linked in: nvme_loop(OE) nvmet(OE) nvme_fabrics(OE) null_blk nvme(OE) nvme_corer
[ 1457.368414]  ata_piix crc32c_intel virtio_pci libata virtio_ring serio_raw t10_pi virtio floppy dm_]
[ 1457.380849] CR2: 0000000000000000
[ 1457.381288] ---[ end trace c6cab61bfd1f68fd ]---
[ 1457.381861] RIP: 0010:blk_mq_free_request+0xe/0x110
[ 1457.382469] Code: 3f ff ff ff 83 f8 01 75 0d 4c 89 e7 e8 1b db ff ff e9 2d ff ff ff 0f 0b eb ef 66 8
[ 1457.384749] RSP: 0018:ffffc900035b7de0 EFLAGS: 00010282
[ 1457.385393] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000002
[ 1457.386264] RDX: ffffffffa060bd05 RSI: 0000000000000000 RDI: 0000000000000000
[ 1457.387142] RBP: 0000000000000037 R08: 0000000000000000 R09: 0000000000000000
[ 1457.388029] R10: 0000000000000000 R11: 000000000000006d R12: 0000000000000000
[ 1457.388914] R13: ffff8887ffa68600 R14: 0000000000000000 R15: ffff8888150564c8
[ 1457.389798] FS:  0000000000000000(0000) GS:ffff888814600000(0000) knlGS:0000000000000000
[ 1457.390796] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1457.391508] CR2: 0000000000000000 CR3: 000000081c0ac000 CR4: 00000000003406e0
[ 1457.392525] Kernel panic - not syncing: Fatal exception
[ 1457.394138] Kernel Offset: disabled
[ 1457.394677] ---[ end Kernel panic - not syncing: Fatal exception ]---

We fix this Oops by adding a new goto label out_put_req and reordering
the blk_put_request call to avoid calling blk_put_request() with rq
value is set to NULL. Here we also update the rest of the code
accordingly.

Fixes: 06b7164dfdc0 ("nvmet: add passthru code to process commands")
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
@TerrenceXu TerrenceXu closed this Sep 16, 2020
@altmnt
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@altmnt altmnt commented Sep 21, 2020

I am experiencing latency on kernel 5.8.10 and qemu built from master branch of the official repo (5.1.50). After setting GUI_REFRESH_INTERVAL_DEFAULT it's all smooth but I fee a general lag about 100-200ms (maybe due to the optimus graphics).
If i set -display gtk,gl=on,show-cursor=on I can see two cursors and guest cursor is delayed by aforementioned interval.
Otherwise performance is good and smooth.
I have also added i915.enable_fbc=0 to the grub but it didnt help

zhenyw pushed a commit that referenced this issue Oct 12, 2020
Get and put the reference to the ctrl in the nvme_dev_open() and
nvme_dev_release() before and after module get/put for ctrl in char
device file operations.

Introduce char_dev relase function, get/put the controller and module
which allows us to fix the potential Oops which can be easily reproduced
with a passthru ctrl (although the problem also exists with pure user
access):

Entering kdb (current=0xffff8887f8290000, pid 3128) on processor 30 Oops: (null)
due to oops @ 0xffffffffa01019ad
CPU: 30 PID: 3128 Comm: bash Tainted: G        W  OE     5.8.0-rc4nvme-5.9+ #35
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.4
RIP: 0010:nvme_free_ctrl+0x234/0x285 [nvme_core]
Code: 57 10 a0 e8 73 bf 02 e1 ba 3d 11 00 00 48 c7 c6 98 33 10 a0 48 c7 c7 1d 57 10 a0 e8 5b bf 02 e1 8
RSP: 0018:ffffc90001d63de0 EFLAGS: 00010246
RAX: ffffffffa05c0440 RBX: ffff8888119e45a0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff8888177e9550 RDI: ffff8888119e43b0
RBP: ffff8887d4768000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: ffffc90001d63c90 R12: ffff8888119e43b0
R13: ffff8888119e5108 R14: dead000000000100 R15: ffff8888119e5108
FS:  00007f1ef27b0740(0000) GS:ffff888817600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffa05c0470 CR3: 00000007f6bee000 CR4: 00000000003406e0
Call Trace:
 device_release+0x27/0x80
 kobject_put+0x98/0x170
 nvmet_passthru_ctrl_disable+0x4a/0x70 [nvmet]
 nvmet_passthru_enable_store+0x4c/0x90 [nvmet]
 configfs_write_file+0xe6/0x150
 vfs_write+0xba/0x1e0
 ksys_write+0x5f/0xe0
 do_syscall_64+0x52/0xb0
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f1ef1eb2840
Code: Bad RIP value.
RSP: 002b:00007fffdbff0eb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007f1ef1eb2840
RDX: 0000000000000002 RSI: 00007f1ef27d2000 RDI: 0000000000000001
RBP: 00007f1ef27d2000 R08: 000000000000000a R09: 00007f1ef27b0740
R10: 0000000000000001 R11: 0000000000000246 R12: 00007f1ef2186400
R13: 0000000000000002 R14: 0000000000000001 R15: 0000000000000000

With this patch fix we take the module ref count in nvme_dev_open() and
release that ref count in newly introduced nvme_dev_release().

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
zhenyw pushed a commit that referenced this issue Apr 15, 2021
Brian Foster reported a lockdep warning on xfs/167:

============================================
WARNING: possible recursive locking detected
5.11.0-rc4 #35 Tainted: G        W I
--------------------------------------------
fsstress/17733 is trying to acquire lock:
ffff8e0fd1d90650 (sb_internal){++++}-{0:0}, at: xfs_free_eofblocks+0x104/0x1d0 [xfs]

but task is already holding lock:
ffff8e0fd1d90650 (sb_internal){++++}-{0:0}, at: xfs_trans_alloc_inode+0x5f/0x160 [xfs]

stack backtrace:
CPU: 38 PID: 17733 Comm: fsstress Tainted: G        W I       5.11.0-rc4 #35
Hardware name: Dell Inc. PowerEdge R740/01KPX8, BIOS 1.6.11 11/20/2018
Call Trace:
 dump_stack+0x8b/0xb0
 __lock_acquire.cold+0x159/0x2ab
 lock_acquire+0x116/0x370
 xfs_trans_alloc+0x1ad/0x310 [xfs]
 xfs_free_eofblocks+0x104/0x1d0 [xfs]
 xfs_blockgc_scan_inode+0x24/0x60 [xfs]
 xfs_inode_walk_ag+0x202/0x4b0 [xfs]
 xfs_inode_walk+0x66/0xc0 [xfs]
 xfs_trans_alloc+0x160/0x310 [xfs]
 xfs_trans_alloc_inode+0x5f/0x160 [xfs]
 xfs_alloc_file_space+0x105/0x300 [xfs]
 xfs_file_fallocate+0x270/0x460 [xfs]
 vfs_fallocate+0x14d/0x3d0
 __x64_sys_fallocate+0x3e/0x70
 do_syscall_64+0x33/0x40
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

The cause of this is the new code that spurs a scan to garbage collect
speculative preallocations if we fail to reserve enough blocks while
allocating a transaction.  While the warning itself is a fairly benign
lockdep complaint, it does expose a potential livelock if the rwsem
behavior ever changes with regards to nesting read locks when someone's
waiting for a write lock.

Fix this by freeing the transaction and jumping back to xfs_trans_alloc
like this patch in the V4 submission[1].

[1] https://lore.kernel.org/linux-xfs/161142798066.2171939.9311024588681972086.stgit@magnolia/

Fixes: a1a7d05 ("xfs: flush speculative space allocations when we run out of space")
Reported-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
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