On Mon, Aug 9, 2021 at 9:36 AM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> Oh, I guess I have to actually download the stable tree. Normally I
> only keep the main tree git around..
Ok, so it does the accounting a bit differently - after allocating
them rather than before - but it actually ends up being a simpler
patch because of that.
I think it ends up like the attached.
UNTESTED.
I'm not 100% convinced we need to backport this that far anyway, but
whatever. Nobody sane runs something like a build server on 4.4.
Nobody sane should run 4.4 at all, of course.
Linus
fs/pipe.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/fs/pipe.c b/fs/pipe.c
index 6534470a6c19..37a003b645ef 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -27,6 +27,21 @@
#include "internal.h"
+/*
+ * New pipe buffers will be restricted to this size while the user is exceeding
+ * their pipe buffer quota. The general pipe use case needs at least two
+ * buffers: one for data yet to be read, and one for new data. If this is less
+ * than two, then a write to a non-empty pipe may block even if the pipe is not
+ * full. This can occur with GNU make jobserver or similar uses of pipes as
+ * semaphores: multiple processes may be waiting to write tokens back to the
+ * pipe before reading tokens: https://lore.kernel.org/lkml/1628086770.5rn8p04n6j.none@localhost/.
+ *
+ * Users can reduce their pipe buffers with F_SETPIPE_SZ below this at their
+ * own risk, namely: pipe writes to non-full pipes may block until the pipe is
+ * emptied.
+ */
+#define PIPE_MIN_DEF_BUFFERS 2
+
/*
* The max size that a non-root user is allowed to grow the pipe. Can
* be set by root in /proc/sys/fs/pipe-max-size
@@ -621,7 +636,7 @@ struct pipe_inode_info *alloc_pipe_info(void)
if (!too_many_pipe_buffers_hard(user)) {
if (too_many_pipe_buffers_soft(user))
- pipe_bufs = 1;
+ pipe_bufs = PIPE_MIN_DEF_BUFFERS;
pipe->bufs = kzalloc(sizeof(struct pipe_buffer) * pipe_bufs, GFP_KERNEL);
}
