Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
pipe: fix and clarify pipe read wakeup logic
This is the read side version of the previous commit: it simplifies the
logic to only wake up waiting writers when necessary, and makes sure to
use a synchronous wakeup. This time not so much for GNU make jobserver
reasons (that pipe never fills up), but simply to get the writer going
quickly again.
A bit less verbose commentary this time, if only because I assume that
the write side commentary isn't going to be ignored if you touch this
code.
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+18
-13
+18
-13
fs/pipe.c
+18
-13
fs/pipe.c
···
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size_t total_len = iov_iter_count(to);
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struct file *filp = iocb->ki_filp;
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struct pipe_inode_info *pipe = filp->private_data;
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-
int do_wakeup;
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+
bool was_full;
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ssize_t ret;
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/* Null read succeeds. */
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if (unlikely(total_len == 0))
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return 0;
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-
do_wakeup = 0;
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ret = 0;
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__pipe_lock(pipe);
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+
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/*
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* We only wake up writers if the pipe was full when we started
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* reading in order to avoid unnecessary wakeups.
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*
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* But when we do wake up writers, we do so using a sync wakeup
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* (WF_SYNC), because we want them to get going and generate more
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* data for us.
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*/
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+
was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
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for (;;) {
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unsigned int head = pipe->head;
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unsigned int tail = pipe->tail;
···
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}
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if (!buf->len) {
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-
bool wake;
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pipe_buf_release(pipe, buf);
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spin_lock_irq(&pipe->wait.lock);
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tail++;
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pipe->tail = tail;
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-
do_wakeup = 1;
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-
wake = head - (tail - 1) == pipe->max_usage / 2;
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-
if (wake)
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-
wake_up_locked_poll(
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-
&pipe->wait, EPOLLOUT | EPOLLWRNORM);
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spin_unlock_irq(&pipe->wait.lock);
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-
if (wake)
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-
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
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}
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total_len -= chars;
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if (!total_len)
···
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ret = -ERESTARTSYS;
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break;
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}
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+
if (was_full) {
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+
wake_up_interruptible_sync_poll(&pipe->wait, EPOLLOUT | EPOLLWRNORM);
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+
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
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+
}
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pipe_wait(pipe);
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+
was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
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}
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__pipe_unlock(pipe);
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-
/* Signal writers asynchronously that there is more room. */
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-
if (do_wakeup) {
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-
wake_up_interruptible_poll(&pipe->wait, EPOLLOUT | EPOLLWRNORM);
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+
if (was_full) {
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+
wake_up_interruptible_sync_poll(&pipe->wait, EPOLLOUT | EPOLLWRNORM);
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kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
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}
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if (ret > 0)