[PATCH] pipe: honor IOCB_NOWAIT

Jens Axboe
2020-09-07T15:26:59Z

Pipe only looks at O_NONBLOCK for non-blocking operation, which means that
io_uring can't easily poll for it or attempt non-blocking issues. Check for
IOCB_NOWAIT in locking the pipe for reads and writes, and ditto when we
decide on whether or not to block or return -EAGAIN.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

If this is acceptable, then I can add S_ISFIFO to the whitelist on file
descriptors we can IOCB_NOWAIT try for, then poll if we get -EAGAIN
instead of using thread offload.

diff --git a/fs/pipe.c b/fs/pipe.c
index 60dbee457143..3cee28e35985 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -82,6 +82,13 @@ void pipe_unlock(struct pipe_inode_info *pipe)
}
EXPORT_SYMBOL(pipe_unlock);

+static inline bool __pipe_lock_nonblock(struct pipe_inode_info *pipe)
+{
+ if (mutex_trylock(&pipe->mutex))
+ return true;
+ return false;
+}
+
static inline void __pipe_lock(struct pipe_inode_info *pipe)
{
mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);
@@ -244,7 +251,12 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
return 0;

ret = 0;
- __pipe_lock(pipe);
+ if (iocb->ki_flags & IOCB_NOWAIT) {
+ if (!__pipe_lock_nonblock(pipe))
+ return -EAGAIN;
+ } else {
+ __pipe_lock(pipe);
+ }

/*
* We only wake up writers if the pipe was full when we started
@@ -344,7 +356,8 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
break;
if (ret)
break;
- if (filp->f_flags & O_NONBLOCK) {
+ if ((filp->f_flags & O_NONBLOCK) ||
+ (iocb->ki_flags & IOCB_NOWAIT)) {
ret = -EAGAIN;
break;
}
@@ -432,7 +445,12 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
if (unlikely(total_len == 0))
return 0;

- __pipe_lock(pipe);
+ if (iocb->ki_flags & IOCB_NOWAIT) {
+ if (!__pipe_lock_nonblock(pipe))
+ return -EAGAIN;
+ } else {
+ __pipe_lock(pipe);
+ }

if (!pipe->readers) {
send_sig(SIGPIPE, current, 0);
@@ -554,7 +572,8 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
continue;

/* Wait for buffer space to become available. */
- if (filp->f_flags & O_NONBLOCK) {
+ if ((filp->f_flags & O_NONBLOCK) ||
+ (iocb->ki_flags & IOCB_NOWAIT)) {
if (!ret)
ret = -EAGAIN;
break;

--
Jens Axboe