![]() | |||||||||||||
Messages in this thread Patch in this message |
Hi Linus,
pipe_write contains a wakeup storm, 2 writers that write into the same
fifo can wake each other up, and spend 100% cpu time with wakeup/schedule,
without making any progress.
The patch below was part of -dj, and IIRC even of -ac, for a few months,
but it's more a rewrite of pipe_read and _write.
Could you merge it, or do you want a minimal fix?
The only regression I'm aware of is that
$ dd if=/dev/zero | grep not_there
will fail due to OOM, because grep does something like
for(;;) {
rlen = read(fd, buf, len);
if (rlen == len) {
len *= 2;
buf = realloc(buf, len);
}
}
if it operates on pipes, and due to the improved syscall merging, read
will always return the maximum possible amount of data. But that's a grep
bug, not a kernel problem.
The diff is older, but applies to 2.5.40 without offsets.
--
Manfred
<<<<<<<<<<<<<<
diff -urpN --exclude-from=/home/davej/.exclude bk-linus/fs/pipe.c linux-2.5/fs/pipe.c
--- bk-linus/fs/pipe.c 2002-08-20 13:15:16.000000000 +0100
+++ linux-2.5/fs/pipe.c 2002-08-20 13:25:24.000000000 +0100
@@ -25,6 +25,9 @@
*
* FIFOs and Pipes now generate SIGIO for both readers and writers.
* -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
+ *
+ * pipe_read & write cleanup
+ * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
*/
/* Drop the inode semaphore and wait for a pipe event, atomically */
@@ -44,97 +47,81 @@ static ssize_t
pipe_read(struct file *filp, char *buf, size_t count, loff_t *ppos)
{
struct inode *inode = filp->f_dentry->d_inode;
- ssize_t size, read, ret;
+ int do_wakeup;
+ ssize_t ret;
- /* Seeks are not allowed on pipes. */
- ret = -ESPIPE;
- read = 0;
- if (ppos != &filp->f_pos)
- goto out_nolock;
+ /* pread is not allowed on pipes. */
+ if (unlikely(ppos != &filp->f_pos))
+ return -ESPIPE;
+
+ /* Null read succeeds. */
+ if (unlikely(count == 0))
+ return 0;
- /* Always return 0 on null read. */
+ do_wakeup = 0;
ret = 0;
- if (count == 0)
- goto out_nolock;
+ down(PIPE_SEM(*inode));
+ for (;;) {
+ int size = PIPE_LEN(*inode);
+ if (size) {
+ char *pipebuf = PIPE_BASE(*inode) + PIPE_START(*inode);
+ ssize_t chars = PIPE_MAX_RCHUNK(*inode);
- /* Get the pipe semaphore */
- ret = -ERESTARTSYS;
- if (down_interruptible(PIPE_SEM(*inode)))
- goto out_nolock;
-
- if (PIPE_EMPTY(*inode)) {
-do_more_read:
- ret = 0;
- if (!PIPE_WRITERS(*inode))
- goto out;
+ if (chars > count)
+ chars = count;
+ if (chars > size)
+ chars = size;
- ret = -EAGAIN;
- if (filp->f_flags & O_NONBLOCK)
- goto out;
-
- for (;;) {
- PIPE_WAITING_READERS(*inode)++;
- pipe_wait(inode);
- PIPE_WAITING_READERS(*inode)--;
- ret = -ERESTARTSYS;
- if (signal_pending(current))
- goto out;
- ret = 0;
- if (!PIPE_EMPTY(*inode))
+ if (copy_to_user(buf, pipebuf, chars)) {
+ if (!ret) ret = -EFAULT;
break;
- if (!PIPE_WRITERS(*inode))
- goto out;
- }
- }
+ }
+ ret += chars;
- /* Read what data is available. */
- ret = -EFAULT;
- while (count > 0 && (size = PIPE_LEN(*inode))) {
- char *pipebuf = PIPE_BASE(*inode) + PIPE_START(*inode);
- ssize_t chars = PIPE_MAX_RCHUNK(*inode);
-
- if (chars > count)
- chars = count;
- if (chars > size)
- chars = size;
-
- if (copy_to_user(buf, pipebuf, chars))
- goto out;
-
- read += chars;
- PIPE_START(*inode) += chars;
- PIPE_START(*inode) &= (PIPE_SIZE - 1);
- PIPE_LEN(*inode) -= chars;
- count -= chars;
- buf += chars;
+ PIPE_START(*inode) += chars;
+ PIPE_START(*inode) &= (PIPE_SIZE - 1);
+ PIPE_LEN(*inode) -= chars;
+ count -= chars;
+ buf += chars;
+ do_wakeup = 1;
+ }
+ if (!count)
+ break; /* common path: read succeeded */
+ if (PIPE_LEN(*inode)) /* test for cyclic buffers */
+ continue;
+ if (!PIPE_WRITERS(*inode))
+ break;
+ if (!PIPE_WAITING_WRITERS(*inode)) {
+ /* syscall merging: Usually we must not sleep
+ * if O_NONBLOCK is set, or if we got some data.
+ * But if a writer sleeps in kernel space, then
+ * we can wait for that data without violating POSIX.
+ */
+ if (ret)
+ break;
+ if (filp->f_flags & O_NONBLOCK) {
+ ret = -EAGAIN;
+ break;
+ }
+ }
+ if (signal_pending(current)) {
+ if (!ret) ret = -ERESTARTSYS;
+ break;
+ }
+ if (do_wakeup) {
+ wake_up_interruptible(PIPE_WAIT(*inode));
+ kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
+ }
+ pipe_wait(inode);
}
-
- /* Cache behaviour optimization */
- if (!PIPE_LEN(*inode))
- PIPE_START(*inode) = 0;
-
- if (count && PIPE_WAITING_WRITERS(*inode) && !(filp->f_flags & O_NONBLOCK)) {
- /*
- * We know that we are going to sleep: signal
- * writers synchronously that there is more
- * room.
- */
+ up(PIPE_SEM(*inode));
+ /* Signal writers asynchronously that there is more room. */
+ if (do_wakeup) {
wake_up_interruptible_sync(PIPE_WAIT(*inode));
- kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
- if (!PIPE_EMPTY(*inode))
- BUG();
- goto do_more_read;
+ kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
}
- /* Signal writers asynchronously that there is more room. */
- wake_up_interruptible(PIPE_WAIT(*inode));
- kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
-
- ret = read;
-out:
- up(PIPE_SEM(*inode));
-out_nolock:
- if (read)
- ret = read;
+ if (ret > 0)
+ UPDATE_ATIME(inode);
return ret;
}
@@ -142,116 +129,90 @@ static ssize_t
pipe_write(struct file *filp, const char *buf, size_t count, loff_t *ppos)
{
struct inode *inode = filp->f_dentry->d_inode;
- ssize_t free, written, ret;
+ ssize_t ret;
+ size_t min;
+ int do_wakeup;
+
+ /* pwrite is not allowed on pipes. */
+ if (unlikely(ppos != &filp->f_pos))
+ return -ESPIPE;
+
+ /* Null write succeeds. */
+ if (unlikely(count == 0))
+ return 0;
- /* Seeks are not allowed on pipes. */
- ret = -ESPIPE;
- written = 0;
- if (ppos != &filp->f_pos)
- goto out_nolock;
-
- /* Null write succeeds. */
+ do_wakeup = 0;
ret = 0;
- if (count == 0)
- goto out_nolock;
-
- ret = -ERESTARTSYS;
- if (down_interruptible(PIPE_SEM(*inode)))
- goto out_nolock;
-
- /* No readers yields SIGPIPE. */
- if (!PIPE_READERS(*inode))
- goto sigpipe;
-
- /* If count <= PIPE_BUF, we have to make it atomic. */
- free = (count <= PIPE_BUF ? count : 1);
-
- /* Wait, or check for, available space. */
- if (filp->f_flags & O_NONBLOCK) {
- ret = -EAGAIN;
- if (PIPE_FREE(*inode) < free)
- goto out;
- } else {
- while (PIPE_FREE(*inode) < free) {
- PIPE_WAITING_WRITERS(*inode)++;
- pipe_wait(inode);
- PIPE_WAITING_WRITERS(*inode)--;
- ret = -ERESTARTSYS;
- if (signal_pending(current))
- goto out;
-
- if (!PIPE_READERS(*inode))
- goto sigpipe;
+ min = count;
+ if (min > PIPE_BUF)
+ min = 1;
+ down(PIPE_SEM(*inode));
+ for (;;) {
+ int free;
+ if (!PIPE_READERS(*inode)) {
+ send_sig(SIGPIPE, current, 0);
+ if (!ret) ret = -EPIPE;
+ break;
}
- }
-
- /* Copy into available space. */
- ret = -EFAULT;
- while (count > 0) {
- int space;
- char *pipebuf = PIPE_BASE(*inode) + PIPE_END(*inode);
- ssize_t chars = PIPE_MAX_WCHUNK(*inode);
-
- if ((space = PIPE_FREE(*inode)) != 0) {
+ free = PIPE_FREE(*inode);
+ if (free >= min) {
+ /* transfer data */
+ ssize_t chars = PIPE_MAX_WCHUNK(*inode);
+ char *pipebuf = PIPE_BASE(*inode) + PIPE_END(*inode);
+ /* Always wakeup, even if the copy fails. Otherwise
+ * we lock up (O_NONBLOCK-)readers that sleep due to
+ * syscall merging.
+ */
+ do_wakeup = 1;
if (chars > count)
chars = count;
- if (chars > space)
- chars = space;
+ if (chars > free)
+ chars = free;
- if (copy_from_user(pipebuf, buf, chars))
- goto out;
+ if (copy_from_user(pipebuf, buf, chars)) {
+ if (!ret) ret = -EFAULT;
+ break;
+ }
- written += chars;
+ ret += chars;
PIPE_LEN(*inode) += chars;
count -= chars;
buf += chars;
- space = PIPE_FREE(*inode);
+ }
+ if (!count)
+ break;
+ if (PIPE_FREE(*inode) && ret) {
+ /* handle cyclic data buffers */
+ min = 1;
continue;
}
-
- ret = written;
- if (filp->f_flags & O_NONBLOCK)
+ if (filp->f_flags & O_NONBLOCK) {
+ if (!ret) ret = -EAGAIN;
break;
-
- do {
- /*
- * Synchronous wake-up: it knows that this process
- * is going to give up this CPU, so it doesn't have
- * to do idle reschedules.
- */
+ }
+ if (signal_pending(current)) {
+ if (!ret) ret = -ERESTARTSYS;
+ break;
+ }
+ if (do_wakeup) {
wake_up_interruptible_sync(PIPE_WAIT(*inode));
- kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
- PIPE_WAITING_WRITERS(*inode)++;
- pipe_wait(inode);
- PIPE_WAITING_WRITERS(*inode)--;
- if (signal_pending(current))
- goto out;
- if (!PIPE_READERS(*inode))
- goto sigpipe;
- } while (!PIPE_FREE(*inode));
- ret = -EFAULT;
+ kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
+ do_wakeup = 0;
+ }
+ PIPE_WAITING_WRITERS(*inode)++;
+ pipe_wait(inode);
+ PIPE_WAITING_WRITERS(*inode)--;
}
-
- /* Signal readers asynchronously that there is more data. */
- wake_up_interruptible(PIPE_WAIT(*inode));
- kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
-
- inode->i_ctime = inode->i_mtime = CURRENT_TIME;
- mark_inode_dirty(inode);
-
-out:
up(PIPE_SEM(*inode));
-out_nolock:
- if (written)
- ret = written;
+ if (do_wakeup) {
+ wake_up_interruptible(PIPE_WAIT(*inode));
+ kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
+ }
+ if (ret > 0) {
+ inode->i_ctime = inode->i_mtime = CURRENT_TIME;
+ mark_inode_dirty(inode);
+ }
return ret;
-
-sigpipe:
- if (written)
- goto out;
- up(PIPE_SEM(*inode));
- send_sig(SIGPIPE, current, 0);
- return -EPIPE;
}
static ssize_t
@@ -525,7 +486,7 @@ struct inode* pipe_new(struct inode* ino
PIPE_BASE(*inode) = (char*) page;
PIPE_START(*inode) = PIPE_LEN(*inode) = 0;
PIPE_READERS(*inode) = PIPE_WRITERS(*inode) = 0;
- PIPE_WAITING_READERS(*inode) = PIPE_WAITING_WRITERS(*inode) = 0;
+ PIPE_WAITING_WRITERS(*inode) = 0;
PIPE_RCOUNTER(*inode) = PIPE_WCOUNTER(*inode) = 1;
*PIPE_FASYNC_READERS(*inode) = *PIPE_FASYNC_WRITERS(*inode) = NULL;
diff -urpN --exclude-from=/home/davej/.exclude bk-linus/include/linux/pipe_fs_i.h linux-2.5/include/linux/pipe_fs_i.h
--- bk-linus/include/linux/pipe_fs_i.h 2002-08-20 13:15:58.000000000 +0100
+++ linux-2.5/include/linux/pipe_fs_i.h 2002-08-20 13:26:25.000000000 +0100
@@ -9,7 +9,6 @@ struct pipe_inode_info {
unsigned int start;
unsigned int readers;
unsigned int writers;
- unsigned int waiting_readers;
unsigned int waiting_writers;
unsigned int r_counter;
unsigned int w_counter;
@@ -28,7 +27,6 @@ struct pipe_inode_info {
#define PIPE_LEN(inode) ((inode).i_pipe->len)
#define PIPE_READERS(inode) ((inode).i_pipe->readers)
#define PIPE_WRITERS(inode) ((inode).i_pipe->writers)
-#define PIPE_WAITING_READERS(inode) ((inode).i_pipe->waiting_readers)
#define PIPE_WAITING_WRITERS(inode) ((inode).i_pipe->waiting_writers)
#define PIPE_RCOUNTER(inode) ((inode).i_pipe->r_counter)
#define PIPE_WCOUNTER(inode) ((inode).i_pipe->w_counter)
--
<<<<<<<<<<<<<<
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
| ||||||||||||
| Last update: 2005-03-22 12:29 [from the cache] ©2003-2008 | |||||||||||||