diff options
author | Alex Xu (Hello71) <alex_y_xu@yahoo.ca> | 2021-08-05 10:40:47 -0400 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-08-15 12:59:56 +0200 |
commit | 7392701d8615e923cc7ce55cd10e7155189a0062 (patch) | |
tree | 96f00bafd213f64b50b4cd8e8251f57b10a4a30b /fs | |
parent | 07d4712300d9e2da54675ce10831a7996b4e939e (diff) |
pipe: increase minimum default pipe size to 2 pages
commit 46c4c9d1beb7f5b4cec4dd90e7728720583ee348 upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/pipe.c | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/fs/pipe.c b/fs/pipe.c index 6534470a6c19..37a003b645ef 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -28,6 +28,21 @@ #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); } |