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-Wtautological-overlap-compare in drivers/infiniband/hw/hfi1/msix.c #841
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-Wtautological-compare
-Wtautological-overlap-compare
[BUG] linux-next
This is an issue only seen in linux-next
[FIXED][LINUX] development cycle
This bug was only present and fixed in a -next or -rc cycle
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nathanchance
added
[PATCH] Submitted
A patch has been submitted for review
[BUG] linux-next
This is an issue only seen in linux-next
-Wtautological-overlap-compare
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Jan 16, 2020
fengguang
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Jan 17, 2020
Clang warns: drivers/infiniband/hw/hfi1/msix.c:136:22: warning: overlapping comparisons always evaluate to false [-Wtautological-overlap-compare] if (type < IRQ_SDMA && type >= IRQ_OTHER) ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~ 1 warning generated. It is impossible for something to be less than 0 (IRQ_SDMA) and greater than or equal to 3 (IRQ_OTHER) at the same time. A logical OR should have been used to keep the same logic as before. Link: ClangBuiltLinux#841 Fixes: 13d2a83 ("IB/hfi1: Decouple IRQ name from type") Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Picked up, I'll close this when it appears in -next: https://lore.kernel.org/lkml/20200125193652.GA30707@jggl/ |
alaahl
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Jan 26, 2020
Clang warns: drivers/infiniband/hw/hfi1/msix.c:136:22: warning: overlapping comparisons always evaluate to false [-Wtautological-overlap-compare] if (type < IRQ_SDMA && type >= IRQ_OTHER) ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~ 1 warning generated. It is impossible for something to be less than 0 (IRQ_SDMA) and greater than or equal to 3 (IRQ_OTHER) at the same time. A logical OR should have been used to keep the same logic as before. Link: https://lore.kernel.org/r/20200116222658.5285-1-natechancellor@gmail.com Link: ClangBuiltLinux#841 Fixes: 13d2a83 ("IB/hfi1: Decouple IRQ name from type") Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Acked-by: Dennis Dalessandro <dennis.dalessandro@intel.com> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Fixed in next-20200128: https://git.kernel.org/next/linux-next/c/79ba4f9310673a8870fda5a062a558923fa65c93 |
nathanchance
added
[FIXED][LINUX] development cycle
This bug was only present and fixed in a -next or -rc cycle
and removed
[PATCH] Submitted
A patch has been submitted for review
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Feb 3, 2020
nathanchance
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Sep 22, 2020
Currently, for hashmap, the bpf iterator will grab a bucket lock, a spinlock, before traversing the elements in the bucket. This can ensure all bpf visted elements are valid. But this mechanism may cause deadlock if update/deletion happens to the same bucket of the visited map in the program. For example, if we added bpf_map_update_elem() call to the same visited element in selftests bpf_iter_bpf_hash_map.c, we will have the following deadlock: ============================================ WARNING: possible recursive locking detected 5.9.0-rc1+ #841 Not tainted -------------------------------------------- test_progs/1750 is trying to acquire lock: ffff9a5bb73c5e70 (&htab->buckets[i].raw_lock){....}-{2:2}, at: htab_map_update_elem+0x1cf/0x410 but task is already holding lock: ffff9a5bb73c5e20 (&htab->buckets[i].raw_lock){....}-{2:2}, at: bpf_hash_map_seq_find_next+0x94/0x120 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&htab->buckets[i].raw_lock); lock(&htab->buckets[i].raw_lock); *** DEADLOCK *** ... Call Trace: dump_stack+0x78/0xa0 __lock_acquire.cold.74+0x209/0x2e3 lock_acquire+0xba/0x380 ? htab_map_update_elem+0x1cf/0x410 ? __lock_acquire+0x639/0x20c0 _raw_spin_lock_irqsave+0x3b/0x80 ? htab_map_update_elem+0x1cf/0x410 htab_map_update_elem+0x1cf/0x410 ? lock_acquire+0xba/0x380 bpf_prog_ad6dab10433b135d_dump_bpf_hash_map+0x88/0xa9c ? find_held_lock+0x34/0xa0 bpf_iter_run_prog+0x81/0x16e __bpf_hash_map_seq_show+0x145/0x180 bpf_seq_read+0xff/0x3d0 vfs_read+0xad/0x1c0 ksys_read+0x5f/0xe0 do_syscall_64+0x33/0x40 entry_SYSCALL_64_after_hwframe+0x44/0xa9 ... The bucket_lock first grabbed in seq_ops->next() called by bpf_seq_read(), and then grabbed again in htab_map_update_elem() in the bpf program, causing deadlocks. Actually, we do not need bucket_lock here, we can just use rcu_read_lock() similar to netlink iterator where the rcu_read_{lock,unlock} likes below: seq_ops->start(): rcu_read_lock(); seq_ops->next(): rcu_read_unlock(); /* next element */ rcu_read_lock(); seq_ops->stop(); rcu_read_unlock(); Compared to old bucket_lock mechanism, if concurrent updata/delete happens, we may visit stale elements, miss some elements, or repeat some elements. I think this is a reasonable compromise. For users wanting to avoid stale, missing/repeated accesses, bpf_map batch access syscall interface can be used. Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200902235340.2001375-1-yhs@fb.com
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Labels
-Wtautological-compare
-Wtautological-overlap-compare
[BUG] linux-next
This is an issue only seen in linux-next
[FIXED][LINUX] development cycle
This bug was only present and fixed in a -next or -rc cycle
Patch sent: https://lore.kernel.org/lkml/20200116222658.5285-1-natechancellor@gmail.com/
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