This is a note to let you know that I've just added the patch titled
io_uring/rw: fix missing NOWAIT check for O_DIRECT start write
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
io_uring-rw-fix-missing-nowait-check-for-o_direct-st.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 7cc8484de2585d9324d89c118dfda19dc847ebab
Author: Jens Axboe <axboe@xxxxxxxxx>
Date: Thu Oct 31 08:05:44 2024 -0600
io_uring/rw: fix missing NOWAIT check for O_DIRECT start write
[ Upstream commit 1d60d74e852647255bd8e76f5a22dc42531e4389 ]
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@xxxxxxxxxxxxxxx # 5.10+
Reported-by: Peter Mann <peter.mann@xxxxx>
Link: https://lore.kernel.org/io-uring/38c94aec-81c9-4f62-b44e-1d87f5597644@xxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/io_uring/rw.c b/io_uring/rw.c
index c15c7873813b3..9d6e17a244ae7 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -839,6 +839,25 @@ int io_read(struct io_kiocb *req, unsigned int issue_flags)
return kiocb_done(req, ret, issue_flags);
}
+static bool io_kiocb_start_write(struct io_kiocb *req, struct kiocb *kiocb)
+{
+ struct inode *inode;
+ bool ret;
+
+ if (!(req->flags & REQ_F_ISREG))
+ return true;
+ if (!(kiocb->ki_flags & IOCB_NOWAIT)) {
+ kiocb_start_write(kiocb);
+ return true;
+ }
+
+ inode = file_inode(kiocb->ki_filp);
+ ret = sb_start_write_trylock(inode->i_sb);
+ if (ret)
+ __sb_writers_release(inode->i_sb, SB_FREEZE_WRITE);
+ return ret;
+}
+
int io_write(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
@@ -892,8 +911,8 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
return ret;
}
- if (req->flags & REQ_F_ISREG)
- kiocb_start_write(kiocb);
+ if (unlikely(!io_kiocb_start_write(req, kiocb)))
+ return -EAGAIN;
kiocb->ki_flags |= IOCB_WRITE;
if (likely(req->file->f_op->write_iter))
