From 838b35bb6a89c36da07ca39520ec071d9250334d Mon Sep 17 00:00:00 2001 From: Jens Axboe <axboe@kernel.dk> Date: Tue, 24 Oct 2023 14:39:06 -0600 Subject: 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> --- io_uring/rw.c | 9 --------- 1 file changed, 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) -- cgit v1.2.3-58-ga151