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Date:   Wed, 24 Mar 2021 15:23:32 +0100
From:   Lukas Schauer <lukas@schauer.dev>
To:     linux-kernel@vger.kernel.org
Cc:     Alan Cox <alan@redhat.com>, David Howells <dhowells@redhat.com>
Subject: [PATCH] fs/pipe: wakeup wr_wait after setting max_usage
Message-ID: <20210324142332.xfcuvuv2lfjkfznn@vista>
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With commit c73be61cede5882f9605a852414db559c0ebedfd a regression was
introduced that would lock up resized pipes under certain conditions.

In that commit resizing the pipe ring size was moved to a different
function, doing that moved the wakeup for pipe->wr_wait before actually
raising pipe->max_usage. If a pipe was full before the resize occured it
would result in the wakeup never actually triggering pipe_write,
resulting in a deadlock.

This patch moves the wakeup for pipe->wr_wait back to the original
pipe_set_size function, after pipe->max_usage has actually been updated.
---
 fs/pipe.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index bfd946a9ad01..58916ad905b4 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1282,8 +1282,6 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
 	pipe->tail = tail;
 	pipe->head = head;

-	/* This might have made more room for writers */
-	wake_up_interruptible(&pipe->wr_wait);
 	return 0;
 }

@@ -1335,6 +1333,10 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)

 	pipe->max_usage = nr_slots;
 	pipe->nr_accounted = nr_slots;
+
+	/* This might have made more room for writers */
+	wake_up_interruptible(&pipe->wr_wait);
+
 	return pipe->max_usage * PAGE_SIZE;

 out_revert_acct:
--
2.31.0


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