Fix broken "pipe: use event aware wakeups" optimization (28e58ee8) · Commits · 戴 / test

Commit ("pipe: use event aware wakeups") optimized the pipe event wakeup calls to avoid wakeups if the events do not match the requested set. However, the optimization was buggy, in that it didn't actually use the correct sets for the events: when we make room for more data to be written, the pipe poll() routine will return both the POLLOUT _and_ POLLWRNORM bits. Similarly for read. And most critically, when a pipe is released, that will potentially result in POLLHUP|POLLERR (depending on whether it was the last reader or writer), not just the regular POLLIN|POLLOUT. This bug showed itself as a hung gnome-screensaver-dialog process, stuck forever (or at least until it was poked by a signal or by being traced) in a poll() system call. Cc: Davide Libenzi <davidel@xmailserver.org> Cc: David S. Miller <davem@davemloft.net> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

fs/pipe.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -441,7 +441,7 @@ redo:
		break;
		}
		if (do_wakeup) {
		wake_up_interruptible_sync_poll(&pipe->wait, POLLOUT);
		wake_up_interruptible_sync_poll(&pipe->wait, POLLOUT \| POLLWRNORM);
		kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
		}
		pipe_wait(pipe);
		@@ -450,7 +450,7 @@ redo:

		/* Signal writers asynchronously that there is more room. */
		if (do_wakeup) {
		wake_up_interruptible_sync_poll(&pipe->wait, POLLOUT);
		wake_up_interruptible_sync_poll(&pipe->wait, POLLOUT \| POLLWRNORM);
		kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
		}
		if (ret > 0)
		@@ -612,7 +612,7 @@ redo2:
		break;
		}
		if (do_wakeup) {
		wake_up_interruptible_sync_poll(&pipe->wait, POLLIN);
		wake_up_interruptible_sync_poll(&pipe->wait, POLLIN \| POLLRDNORM);
		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
		do_wakeup = 0;
		}
		@@ -623,7 +623,7 @@ redo2:
		out:
		mutex_unlock(&inode->i_mutex);
		if (do_wakeup) {
		wake_up_interruptible_sync_poll(&pipe->wait, POLLIN);
		wake_up_interruptible_sync_poll(&pipe->wait, POLLIN \| POLLRDNORM);
		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
		}
		if (ret > 0)
		@@ -715,7 +715,7 @@ pipe_release(struct inode *inode, int decr, int decw)
		if (!pipe->readers && !pipe->writers) {
		free_pipe_info(inode);
		} else {
		wake_up_interruptible_sync_poll(&pipe->wait, POLLIN \| POLLOUT);
		wake_up_interruptible_sync_poll(&pipe->wait, POLLIN \| POLLOUT \| POLLRDNORM \| POLLWRNORM \| POLLERR \| POLLHUP);
		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
		kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
		}

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