[PATCH] pipe: increase minimum default pipe size to 2 pages
From: Alex Xu (Hello71) <hidden>
Date: 2021-08-05 14:40:57
Also in:
linux-api, linux-fsdevel, stable
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
Possibly related (same subject, not in this thread)
- 2021-08-05 · [PATCH] pipe: increase minimum default pipe size to 2 pages · Alex Xu (Hello71) <hidden>
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: <redacted>
Link: https://lore.kernel.org/lkml/1628086770.5rn8p04n6j.none@localhost/ (local)
Link: https://lore.kernel.org/lkml/1628127094.lxxn016tj7.none@localhost/ (local)
Signed-off-by: Alex Xu (Hello71) <redacted>
---
fs/pipe.c | 19 +++++++++++++++++--
1 file 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@@ -31,6 +31,21 @@ #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())
--
2.32.0