tree aa82038850cca07c84aa766db84b6ddf30e3ded7
parent 617a89484debcd4e7999796d693cf0b77d2519de
author Pavel Begunkov <asml.silence@gmail.com> 1637937495 +0000
committer Jens Axboe <axboe@kernel.dk> 1637940957 -0700

io_uring: fix link traversal locking

WARNING: inconsistent lock state
5.16.0-rc2-syzkaller #0 Not tainted
inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
ffff888078e11418 (&ctx->timeout_lock
){?.+.}-{2:2}
, at: io_timeout_fn+0x6f/0x360 fs/io_uring.c:5943
{HARDIRQ-ON-W} state was registered at:
  [...]
  spin_unlock_irq include/linux/spinlock.h:399 [inline]
  __io_poll_remove_one fs/io_uring.c:5669 [inline]
  __io_poll_remove_one fs/io_uring.c:5654 [inline]
  io_poll_remove_one+0x236/0x870 fs/io_uring.c:5680
  io_poll_remove_all+0x1af/0x235 fs/io_uring.c:5709
  io_ring_ctx_wait_and_kill+0x1cc/0x322 fs/io_uring.c:9534
  io_uring_release+0x42/0x46 fs/io_uring.c:9554
  __fput+0x286/0x9f0 fs/file_table.c:280
  task_work_run+0xdd/0x1a0 kernel/task_work.c:164
  exit_task_work include/linux/task_work.h:32 [inline]
  do_exit+0xc14/0x2b40 kernel/exit.c:832

674ee8e1b4a41 ("io_uring: correct link-list traversal locking") fixed a
data race but introduced a possible deadlock and inconsistentcy in irq
states. E.g.

io_poll_remove_all()
    spin_lock_irq(timeout_lock)
    io_poll_remove_one()
        spin_lock/unlock_irq(poll_lock);
    spin_unlock_irq(timeout_lock)

Another type of problem is freeing a request while holding
->timeout_lock, which may leads to a deadlock in
io_commit_cqring() -> io_flush_timeouts() and other places.

Having 3 nested locks is also too ugly. Add io_match_task_safe(), which
would briefly take and release timeout_lock for race prevention inside,
so the actuall request cancellation / free / etc. code doesn't have it
taken.

Reported-by: syzbot+ff49a3059d49b0ca0eec@syzkaller.appspotmail.com
Reported-by: syzbot+847f02ec20a6609a328b@syzkaller.appspotmail.com
Reported-by: syzbot+3368aadcd30425ceb53b@syzkaller.appspotmail.com
Reported-by: syzbot+51ce8887cdef77c9ac83@syzkaller.appspotmail.com
Reported-by: syzbot+3cb756a49d2f394a9ee3@syzkaller.appspotmail.com
Fixes: 674ee8e1b4a41 ("io_uring: correct link-list traversal locking")
Cc: stable@kernel.org # 5.15+
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/397f7ebf3f4171f1abe41f708ac1ecb5766f0b68.1637937097.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>