linux-kernel - Re: [PATCH 1/3] pipe: drop an always true check in anon_pipe

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Message-ID: <20250304140726.GD26141@redhat.com>
Date: Tue, 4 Mar 2025 15:07:27 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: torvalds@...ux-foundation.org, brauner@...nel.org, mingo@...hat.com,
	peterz@...radead.org, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/3] pipe: drop an always true check in anon_pipe_write()

On 03/04, Mateusz Guzik wrote:
>
> @@ -529,10 +529,9 @@ anon_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;
> +		}

Reviewed-by: Oleg Nesterov <oleg@...hat.com>



It seems that we can also remove the unnecessary signal_pending()
check, but I need to recheck and we need to cleanup the poll_usage
logic first.

This will also remove the unnecessary wakeups when the writer is
interrupted by signal/

diff --git a/fs/pipe.c b/fs/pipe.c
index b0641f75b1ba..ed55a86ca03b 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -541,12 +541,6 @@ anon_pipe_write(struct kiocb *iocb, struct iov_iter *from)
 				ret = -EAGAIN;
 			break;
 		}
-		if (signal_pending(current)) {
-			if (!ret)
-				ret = -ERESTARTSYS;
-			break;
-		}
-
 		/*
 		 * We're going to release the pipe lock and wait for more
 		 * space. We wake up any readers if necessary, and then
@@ -554,10 +548,11 @@ anon_pipe_write(struct kiocb *iocb, struct iov_iter *from)
 		 * become empty while we dropped the lock.
 		 */
 		mutex_unlock(&pipe->mutex);
-		if (was_empty)
+		if (was_empty || pipe->poll_usage)
 			wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
 		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
-		wait_event_interruptible_exclusive(pipe->wr_wait, pipe_writable(pipe));
+		if (wait_event_interruptible_exclusive(pipe->wr_wait, pipe_writable(pipe)) < 0)
+			return ret ?: -ERESTARTSYS;
 		mutex_lock(&pipe->mutex);
 		was_empty = pipe_empty(pipe->head, pipe->tail);
 		wake_next_writer = true;