[PATCH 0/2] Two cleanups to pipe

[PATCH 0/2] Two cleanups to pipe

[Kemeng Shi]

This series tries to remove some unnecessary check in pipe. More details
can be found in respective patches. Thanks!

Kemeng Shi (2):
  pipe: remove pipe_full check with wrong head in pipe_write
  pipe: avoid repeat check of pipe->readers under pipe_lock

 fs/pipe.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

-- 
2.30.0

[PATCH 1/2] pipe: remove pipe_full check with wrong head in pipe_write

[Kemeng Shi]

In pipe_write we have:
	head = pipe->head;
	if (!pipe_full(head, pipe->tail, pipe->max_usage))
		pipe->head = head + 1;
		/* write data to buffer at head */

	/* supposed to check if pipe is full after write */
	if (!pipe_full(head, pipe->tail, pipe->max_usage))
		continue

The second pipe_full expects head after write but head before write is
used. Luckily, we will call pipe_full with correct reloaded pipe->head
in new loop cycle and stop writing correctly. Remove wrong pipe_full
check and simply continue to first pipe_full check after write done to
avoid unnecessary check.

Fixes: a194dfe6e6f6 ("pipe: Rearrange sequence in pipe_write() to preallocate slot")
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 fs/pipe.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 2d88f73f585a..b19875720ff1 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -542,10 +542,9 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 
 			if (!iov_iter_count(from))
 				break;
-		}
 
-		if (!pipe_full(head, pipe->tail, pipe->max_usage))
 			continue;
+		}
 
 		/* Wait for buffer space to become available. */
 		if ((filp->f_flags & O_NONBLOCK) ||
-- 
2.30.0

[PATCH 2/2] pipe: avoid repeat check of pipe->readers with pipe lock held

[Kemeng Shi]

Change to pipe->readers is protected by pipe_lock. Only recheck
pipe->reader after relock to avoid repeat check of pipe->readers with
pipe lock held.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 fs/pipe.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index b19875720ff1..e9c63f66d1c7 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -479,13 +479,6 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 	}
 
 	for (;;) {
-		if (!pipe->readers) {
-			send_sig(SIGPIPE, current, 0);
-			if (!ret)
-				ret = -EPIPE;
-			break;
-		}
-
 		head = pipe->head;
 		if (!pipe_full(head, pipe->tail, pipe->max_usage)) {
 			unsigned int mask = pipe->ring_size - 1;
@@ -573,6 +566,12 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 		__pipe_lock(pipe);
 		was_empty = pipe_empty(pipe->head, pipe->tail);
 		wake_next_writer = true;
+		if (!pipe->readers) {
+			send_sig(SIGPIPE, current, 0);
+			if (!ret)
+				ret = -EPIPE;
+			break;
+		}
 	}
 out:
 	if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
-- 
2.30.0

[PATCH 0/2] Two cleanups to pipe

[Kemeng Shi]

This series tries to remove some unnecessary check in pipe. More details
can be found in respective patches. Thanks!

Kemeng Shi (2):
  pipe: remove pipe_full check with wrong head in pipe_write
  pipe: avoid repeat check of pipe->readers under pipe_lock

 fs/pipe.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

-- 
2.30.0

[PATCH 2/2] pipe: avoid repeat check of pipe->readers with pipe lock held

[Kemeng Shi]

Change to pipe->readers is protected by pipe_lock. Only recheck
pipe->reader after relock to avoid repeat check of pipe->readers with
pipe lock held.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 fs/pipe.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index b19875720ff1..e9c63f66d1c7 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -479,13 +479,6 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 	}
 
 	for (;;) {
-		if (!pipe->readers) {
-			send_sig(SIGPIPE, current, 0);
-			if (!ret)
-				ret = -EPIPE;
-			break;
-		}
-
 		head = pipe->head;
 		if (!pipe_full(head, pipe->tail, pipe->max_usage)) {
 			unsigned int mask = pipe->ring_size - 1;
@@ -573,6 +566,12 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 		__pipe_lock(pipe);
 		was_empty = pipe_empty(pipe->head, pipe->tail);
 		wake_next_writer = true;
+		if (!pipe->readers) {
+			send_sig(SIGPIPE, current, 0);
+			if (!ret)
+				ret = -EPIPE;
+			break;
+		}
 	}
 out:
 	if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
-- 
2.30.0