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1d60d74e85
When io_uring starts a write, it'll call kiocb_start_write() to bump the
super block rwsem, preventing any freezes from happening while that
write is in-flight. The freeze side will grab that rwsem for writing,
excluding any new writers from happening and waiting for existing writes
to finish. But io_uring unconditionally uses kiocb_start_write(), which
will block if someone is currently attempting to freeze the mount point.
This causes a deadlock where freeze is waiting for previous writes to
complete, but the previous writes cannot complete, as the task that is
supposed to complete them is blocked waiting on starting a new write.
This results in the following stuck trace showing that dependency with
the write blocked starting a new write:
task:fio state:D stack:0 pid:886 tgid:886 ppid:876
Call trace:
__switch_to+0x1d8/0x348
__schedule+0x8e8/0x2248
schedule+0x110/0x3f0
percpu_rwsem_wait+0x1e8/0x3f8
__percpu_down_read+0xe8/0x500
io_write+0xbb8/0xff8
io_issue_sqe+0x10c/0x1020
io_submit_sqes+0x614/0x2110
__arm64_sys_io_uring_enter+0x524/0x1038
invoke_syscall+0x74/0x268
el0_svc_common.constprop.0+0x160/0x238
do_el0_svc+0x44/0x60
el0_svc+0x44/0xb0
el0t_64_sync_handler+0x118/0x128
el0t_64_sync+0x168/0x170
INFO: task fsfreeze:7364 blocked for more than 15 seconds.
Not tainted 6.12.0-rc5-00063-g76aaf945701c #7963
with the attempting freezer stuck trying to grab the rwsem:
task:fsfreeze state:D stack:0 pid:7364 tgid:7364 ppid:995
Call trace:
__switch_to+0x1d8/0x348
__schedule+0x8e8/0x2248
schedule+0x110/0x3f0
percpu_down_write+0x2b0/0x680
freeze_super+0x248/0x8a8
do_vfs_ioctl+0x149c/0x1b18
__arm64_sys_ioctl+0xd0/0x1a0
invoke_syscall+0x74/0x268
el0_svc_common.constprop.0+0x160/0x238
do_el0_svc+0x44/0x60
el0_svc+0x44/0xb0
el0t_64_sync_handler+0x118/0x128
el0t_64_sync+0x168/0x170
Fix this by having the io_uring side honor IOCB_NOWAIT, and only attempt a
blocking grab of the super block rwsem if it isn't set. For normal issue
where IOCB_NOWAIT would always be set, this returns -EAGAIN which will
have io_uring core issue a blocking attempt of the write. That will in
turn also get completions run, ensuring forward progress.
Since freezing requires CAP_SYS_ADMIN in the first place, this isn't
something that can be triggered by a regular user.
Cc: stable@vger.kernel.org # 5.10+
Reported-by: Peter Mann <peter.mann@sh.cz>
Link: https://lore.kernel.org/io-uring/38c94aec-81c9-4f62-b44e-1d87f5597644@sh.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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| .. | ||
| advise.c | ||
| advise.h | ||
| alloc_cache.h | ||
| cancel.c | ||
| cancel.h | ||
| epoll.c | ||
| epoll.h | ||
| eventfd.c | ||
| eventfd.h | ||
| fdinfo.c | ||
| fdinfo.h | ||
| filetable.c | ||
| filetable.h | ||
| fs.c | ||
| fs.h | ||
| futex.c | ||
| futex.h | ||
| io_uring.c | ||
| io_uring.h | ||
| io-wq.c | ||
| io-wq.h | ||
| kbuf.c | ||
| kbuf.h | ||
| Makefile | ||
| memmap.c | ||
| memmap.h | ||
| msg_ring.c | ||
| msg_ring.h | ||
| napi.c | ||
| napi.h | ||
| net.c | ||
| net.h | ||
| nop.c | ||
| nop.h | ||
| notif.c | ||
| notif.h | ||
| opdef.c | ||
| opdef.h | ||
| openclose.c | ||
| openclose.h | ||
| poll.c | ||
| poll.h | ||
| refs.h | ||
| register.c | ||
| register.h | ||
| rsrc.c | ||
| rsrc.h | ||
| rw.c | ||
| rw.h | ||
| slist.h | ||
| splice.c | ||
| splice.h | ||
| sqpoll.c | ||
| sqpoll.h | ||
| statx.c | ||
| statx.h | ||
| sync.c | ||
| sync.h | ||
| tctx.c | ||
| tctx.h | ||
| timeout.c | ||
| timeout.h | ||
| truncate.c | ||
| truncate.h | ||
| uring_cmd.c | ||
| uring_cmd.h | ||
| waitid.c | ||
| waitid.h | ||
| xattr.c | ||
| xattr.h | ||