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Commit ac23a173 authored by Alex Xu (Hello71)'s avatar Alex Xu (Hello71) Committed by Greg Kroah-Hartman
Browse files

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: 759c0114 ("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: default avatarAlex Xu (Hello71) <alex_y_xu@yahoo.ca>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f3cae04b

fs/pipe.c

+17 −2
Original line number Diff line number Diff line
@@ -30,6 +30,21 @@ 


#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
@@ -666,8 +681,8 @@ 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) && 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) && is_unprivileged_user())