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authorAlex Xu (Hello71) <alex_y_xu@yahoo.ca>2021-08-05 17:40:47 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-08-05 20:30:47 +0300
commit46c4c9d1beb7f5b4cec4dd90e7728720583ee348 (patch)
tree6d5426934082c44e01e7155bac460d76b342f544
parent251a1524293d0a90c4d5060f65f42a3016280049 (diff)
downloadlinux-46c4c9d1beb7f5b4cec4dd90e7728720583ee348.tar.xz
pipe: increase minimum default pipe size to 2 pages
This program always prints 4096 and hangs before the patch, and always prints 8192 and exits successfully after: int main() { int pipefd[2]; for (int i = 0; i < 1025; i++) if (pipe(pipefd) == -1) return 1; size_t bufsz = fcntl(pipefd[1], F_GETPIPE_SZ); printf("%zd\n", bufsz); char *buf = calloc(bufsz, 1); write(pipefd[1], buf, bufsz); read(pipefd[0], buf, bufsz-1); write(pipefd[1], buf, 1); } Note that you may need to increase your RLIMIT_NOFILE before running the program. Fixes: 759c01142a ("pipe: limit the per-user amount of pages allocated in pipes") Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/lkml/1628086770.5rn8p04n6j.none@localhost/ Link: https://lore.kernel.org/lkml/1628127094.lxxn016tj7.none@localhost/ Signed-off-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/pipe.c19
1 files changed, 17 insertions, 2 deletions
diff --git a/fs/pipe.c b/fs/pipe.c
index 9ef4231cce61..8e6ef62aeb1c 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -32,6 +32,21 @@
#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
*/
@@ -781,8 +796,8 @@ struct pipe_inode_info *alloc_pipe_info(void)
user_bufs = account_pipe_buffers(user, 0, pipe_bufs);
if (too_many_pipe_buffers_soft(user_bufs) && pipe_is_unprivileged_user()) {
- user_bufs = account_pipe_buffers(user, pipe_bufs, 1);
- pipe_bufs = 1;
+ user_bufs = account_pipe_buffers(user, pipe_bufs, PIPE_MIN_DEF_BUFFERS);
+ pipe_bufs = PIPE_MIN_DEF_BUFFERS;
}
if (too_many_pipe_buffers_hard(user_bufs) && pipe_is_unprivileged_user())