Commit d9f21b36 authored by Kuniyuki Iwashima's avatar Kuniyuki Iwashima Committed by Jakub Kicinski
Browse files

af_unix: Try to run GC async. 



If more than 16000 inflight AF_UNIX sockets exist and the garbage
collector is not running, unix_(dgram|stream)_sendmsg() call unix_gc().
Also, they wait for unix_gc() to complete.

In unix_gc(), all inflight AF_UNIX sockets are traversed at least once,
and more if they are the GC candidate.  Thus, sendmsg() significantly
slows down with too many inflight AF_UNIX sockets.

However, if a process sends data with no AF_UNIX FD, the sendmsg() call
does not need to wait for GC.  After this change, only the process that
meets the condition below will be blocked under such a situation.

  1) cmsg contains AF_UNIX socket
  2) more than 32 AF_UNIX sent by the same user are still inflight

Note that even a sendmsg() call that does not meet the condition but has
AF_UNIX FD will be blocked later in unix_scm_to_skb() by the spinlock,
but we allow that as a bonus for sane users.

The results below are the time spent in unix_dgram_sendmsg() sending 1
byte of data with no FD 4096 times on a host where 32K inflight AF_UNIX
sockets exist.

Without series: the sane sendmsg() needs to wait gc unreasonably.

  $ sudo /usr/share/bcc/tools/funclatency -p 11165 unix_dgram_sendmsg
  Tracing 1 functions for "unix_dgram_sendmsg"... Hit Ctrl-C to end.
  ^C
       nsecs               : count     distribution
  [...]
      524288 -> 1048575    : 0        |                                        |
     1048576 -> 2097151    : 3881     |****************************************|
     2097152 -> 4194303    : 214      |**                                      |
     4194304 -> 8388607    : 1        |                                        |

  avg = 1825567 nsecs, total: 7477526027 nsecs, count: 4096

With series: the sane sendmsg() can finish much faster.

  $ sudo /usr/share/bcc/tools/funclatency -p 8702  unix_dgram_sendmsg
  Tracing 1 functions for "unix_dgram_sendmsg"... Hit Ctrl-C to end.
  ^C
       nsecs               : count     distribution
  [...]
         128 -> 255        : 0        |                                        |
         256 -> 511        : 4092     |****************************************|
         512 -> 1023       : 2        |                                        |
        1024 -> 2047       : 0        |                                        |
        2048 -> 4095       : 0        |                                        |
        4096 -> 8191       : 1        |                                        |
        8192 -> 16383      : 1        |                                        |

  avg = 410 nsecs, total: 1680510 nsecs, count: 4096

Signed-off-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20240123170856.41348-6-kuniyu@amazon.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 8b90a9f8

include/net/af_unix.h

+10 −2
Original line number Diff line number Diff line
@@ -8,13 +8,21 @@ 
#include <linux/refcount.h>

#include <net/sock.h>



#if IS_ENABLED(CONFIG_UNIX)

struct unix_sock *unix_get_socket(struct file *filp);

#else

static inline struct unix_sock *unix_get_socket(struct file *filp)

{

	return NULL;

}

#endif



void unix_inflight(struct user_struct *user, struct file *fp);

void unix_notinflight(struct user_struct *user, struct file *fp);

void unix_destruct_scm(struct sk_buff *skb);

void io_uring_destruct_scm(struct sk_buff *skb);

void unix_gc(void);

void wait_for_unix_gc(void);

struct unix_sock *unix_get_socket(struct file *filp);

void wait_for_unix_gc(struct scm_fp_list *fpl);

struct sock *unix_peer_get(struct sock *sk);



#define UNIX_HASH_MOD	(256 - 1)

include/net/scm.h

+1 −0
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ struct scm_creds { 


struct scm_fp_list {

	short			count;

	short			count_unix;

	short			max;

	struct user_struct	*user;

	struct file		*fp[SCM_MAX_FD];

net/core/scm.c

+5 −0
Original line number Diff line number Diff line
@@ -36,6 +36,7 @@ 
#include <net/compat.h>

#include <net/scm.h>

#include <net/cls_cgroup.h>

#include <net/af_unix.h>





/*
@@ -85,6 +86,7 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp) 
			return -ENOMEM;

		*fplp = fpl;

		fpl->count = 0;

		fpl->count_unix = 0;

		fpl->max = SCM_MAX_FD;

		fpl->user = NULL;

	}
@@ -109,6 +111,9 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp) 
			fput(file);

			return -EINVAL;

		}

		if (unix_get_socket(file))

			fpl->count_unix++;



		*fpp++ = file;

		fpl->count++;

	}

net/unix/af_unix.c

+4 −2
Original line number Diff line number Diff line
@@ -1923,11 +1923,12 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg, 
	long timeo;

	int err;



	wait_for_unix_gc();

	err = scm_send(sock, msg, &scm, false);

	if (err < 0)

		return err;



	wait_for_unix_gc(scm.fp);



	err = -EOPNOTSUPP;

	if (msg->msg_flags&MSG_OOB)

		goto out;
@@ -2199,11 +2200,12 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg, 
	bool fds_sent = false;

	int data_len;



	wait_for_unix_gc();

	err = scm_send(sock, msg, &scm, false);

	if (err < 0)

		return err;



	wait_for_unix_gc(scm.fp);



	err = -EOPNOTSUPP;

	if (msg->msg_flags & MSG_OOB) {

#if IS_ENABLED(CONFIG_AF_UNIX_OOB)

net/unix/garbage.c

+9 −1
Original line number Diff line number Diff line
@@ -311,8 +311,9 @@ void unix_gc(void) 
}



#define UNIX_INFLIGHT_TRIGGER_GC 16000

#define UNIX_INFLIGHT_SANE_USER (SCM_MAX_FD * 8)



void wait_for_unix_gc(void)

void wait_for_unix_gc(struct scm_fp_list *fpl)

{

	/* If number of inflight sockets is insane,

	 * force a garbage collect right now.
@@ -324,6 +325,13 @@ void wait_for_unix_gc(void) 
	    !READ_ONCE(gc_in_progress))

		unix_gc();



	/* Penalise users who want to send AF_UNIX sockets

	 * but whose sockets have not been received yet.

	 */

	if (!fpl || !fpl->count_unix ||

	    READ_ONCE(fpl->user->unix_inflight) < UNIX_INFLIGHT_SANE_USER)

		return;



	if (READ_ONCE(gc_in_progress))

		flush_work(&unix_gc_work);

}