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| author | Jens Axboe <axboe@kernel.dk> | 2023-10-24 14:39:06 -0600 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2023-10-25 08:02:29 -0600 |
| commit | 838b35bb6a89c36da07ca39520ec071d9250334d (patch) | |
| tree | 598273089e020a7108b9957be3d277d96f09df0a /io_uring | |
| parent | 7644b1a1c9a7ae8ab99175989bfc8676055edb46 (diff) | |
| download | lwn-838b35bb6a89c36da07ca39520ec071d9250334d.tar.gz lwn-838b35bb6a89c36da07ca39520ec071d9250334d.zip | |
io_uring/rw: disable IOCB_DIO_CALLER_COMP
If an application does O_DIRECT writes with io_uring and the file system
supports IOCB_DIO_CALLER_COMP, then completions of the dio write side is
done from the task_work that will post the completion event for said
write as well.
Whenever a dio write is done against a file, the inode i_dio_count is
elevated. This enables other callers to use inode_dio_wait() to wait for
previous writes to complete. If we defer the full dio completion to
task_work, we are dependent on that task_work being run before the
inode i_dio_count can be decremented.
If the same task that issues io_uring dio writes with
IOCB_DIO_CALLER_COMP performs a synchronous system call that calls
inode_dio_wait(), then we can deadlock as we're blocked sleeping on
the event to become true, but not processing the completions that will
result in the inode i_dio_count being decremented.
Until we can guarantee that this is the case, then disable the deferred
caller completions.
Fixes: 099ada2c8726 ("io_uring/rw: add write support for IOCB_DIO_CALLER_COMP")
Reported-by: Andres Freund <andres@anarazel.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'io_uring')
| -rw-r--r-- | io_uring/rw.c | 9 |
1 files changed, 0 insertions, 9 deletions
diff --git a/io_uring/rw.c b/io_uring/rw.c index c8c822fa7980..807d83ab756e 100644 --- a/io_uring/rw.c +++ b/io_uring/rw.c @@ -913,15 +913,6 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags) kiocb_start_write(kiocb); kiocb->ki_flags |= IOCB_WRITE; - /* - * For non-polled IO, set IOCB_DIO_CALLER_COMP, stating that our handler - * groks deferring the completion to task context. This isn't - * necessary and useful for polled IO as that can always complete - * directly. - */ - if (!(kiocb->ki_flags & IOCB_HIPRI)) - kiocb->ki_flags |= IOCB_DIO_CALLER_COMP; - if (likely(req->file->f_op->write_iter)) ret2 = call_write_iter(req->file, kiocb, &s->iter); else if (req->file->f_op->write) |