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Add MNTK_LOOKUP_EXCL_DOTDOT struct mount flag, which specifies to the

lookup code that dotdot lookups shall override any shared lock
requests with the exclusive one. The flag is useful for filesystems
which sometimes need to upgrade shared lock to exclusive inside the
VOP_LOOKUP or later, which cannot be done safely for dotdot, due to
dvp also locked and causing LOR.

In collaboration with:	    pho
MFC after:	3 weeks


git-svn-id: svn+ssh://svn.freebsd.org/base/head@240283 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
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1 parent 17c2970 commit 69b5e424fcbf44d3cbff1ae77eeec4bcfc9a3928 kib committed Sep 9, 2012
Showing with 14 additions and 9 deletions.
  1. +13 −9 sys/kern/vfs_lookup.c
  2. +1 −0 sys/sys/mount.h
View
22 sys/kern/vfs_lookup.c
@@ -406,11 +406,13 @@ namei(struct nameidata *ndp)
}
static int
-compute_cn_lkflags(struct mount *mp, int lkflags)
+compute_cn_lkflags(struct mount *mp, int lkflags, int cnflags)
{
- if (mp == NULL ||
- ((lkflags & LK_SHARED) && !(mp->mnt_kern_flag & MNTK_LOOKUP_SHARED))) {
+ if (mp == NULL || ((lkflags & LK_SHARED) &&
+ (!(mp->mnt_kern_flag & MNTK_LOOKUP_SHARED) ||
+ ((cnflags & ISDOTDOT) &&
+ (mp->mnt_kern_flag & MNTK_LOOKUP_EXCL_DOTDOT))))) {
lkflags &= ~LK_SHARED;
lkflags |= LK_EXCLUSIVE;
}
@@ -539,7 +541,8 @@ lookup(struct nameidata *ndp)
dp = ndp->ni_startdir;
ndp->ni_startdir = NULLVP;
vn_lock(dp,
- compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags | LK_RETRY));
+ compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags | LK_RETRY,
+ cnp->cn_flags));
dirloop:
/*
@@ -700,7 +703,7 @@ lookup(struct nameidata *ndp)
VFS_UNLOCK_GIANT(tvfslocked);
vn_lock(dp,
compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags |
- LK_RETRY));
+ LK_RETRY, ISDOTDOT));
}
}
@@ -738,7 +741,8 @@ lookup(struct nameidata *ndp)
vprint("lookup in", dp);
#endif
lkflags_save = cnp->cn_lkflags;
- cnp->cn_lkflags = compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags);
+ cnp->cn_lkflags = compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags,
+ cnp->cn_flags);
if ((error = VOP_LOOKUP(dp, &ndp->ni_vp, cnp)) != 0) {
cnp->cn_lkflags = lkflags_save;
KASSERT(ndp->ni_vp == NULL, ("leaf should be empty"));
@@ -757,7 +761,7 @@ lookup(struct nameidata *ndp)
VFS_UNLOCK_GIANT(tvfslocked);
vn_lock(dp,
compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags |
- LK_RETRY));
+ LK_RETRY, cnp->cn_flags));
goto unionlookup;
}
@@ -829,8 +833,8 @@ lookup(struct nameidata *ndp)
dvfslocked = 0;
vref(vp_crossmp);
ndp->ni_dvp = vp_crossmp;
- error = VFS_ROOT(mp, compute_cn_lkflags(mp, cnp->cn_lkflags),
- &tdp);
+ error = VFS_ROOT(mp, compute_cn_lkflags(mp, cnp->cn_lkflags,
+ cnp->cn_flags), &tdp);
vfs_unbusy(mp);
if (vn_lock(vp_crossmp, LK_SHARED | LK_NOWAIT))
panic("vp_crossmp exclusively locked or reclaimed");
View
1 sys/sys/mount.h
@@ -373,6 +373,7 @@ void __mnt_vnode_markerfree(struct vnode **mvp, struct mount *mp);
#define MNTK_NO_IOPF 0x00000100 /* Disallow page faults during reads
and writes. Filesystem shall properly
handle i/o state on EFAULT. */
+#define MNTK_LOOKUP_EXCL_DOTDOT 0x00000800
#define MNTK_NOASYNC 0x00800000 /* disable async */
#define MNTK_UNMOUNT 0x01000000 /* unmount in progress */
#define MNTK_MWAIT 0x02000000 /* waiting for unmount to finish */

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