Re: [PATCH] unix: avoid use-after-free in ep_remove_wait_queue (w/ Fixes:)

From: Rainer Weikusat
Date: Wed Nov 18 2015 - 13:16:10 EST

David Miller <davem@xxxxxxxxxxxxx> writes:
> From: Rainer Weikusat <rweikusat@xxxxxxxxxxxxxxxxxxxxxxx>
> Date: Mon, 16 Nov 2015 22:28:40 +0000
>> An AF_UNIX datagram socket being the client in an n:1


> So because of a corner case of epoll handling and sender socket release,
> every single datagram sendmsg has to do a double lock now?
> I do not dispute the correctness of your fix at this point, but that
> added cost in the fast path is really too high.

Some more information on this: Running the test program included below
on my 'work' system (otherwise idle, after logging in via VT with no GUI
running)/ quadcore AMD A10-5700, 3393.984 for 20 times/ patched 4.3 resulted in the
following throughput statistics[*]:

avg 13.617 M/s
median 13.393 M/s
max 17.14 M/s
min 13.047 M/s
deviation 0.85

I'll try to post the results for 'unpatched' later as I'm also working
on a couple of other things.

[*] I do not use my fingers for counting, hence, these are binary and
not decimal units.

#include <inttypes.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <unistd.h>

enum {
MSG_SZ = 16,
MSGS = 1000000

static char msg[MSG_SZ];

static uint64_t tv2u(struct timeval *tv)
uint64_t u;

u = tv->tv_sec;
u *= 1000000;
return u + tv->tv_usec;

int main(void)
struct timeval start, stop;
uint64_t t_diff;
double rate;
int sks[2];
unsigned remain;
char buf[MSG_SZ];

socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sks);

if (fork() == 0) {

gettimeofday(&start, 0);
while (read(sks[1], buf, sizeof(buf)) > 0);
gettimeofday(&stop, 0);

t_diff = tv2u(&stop);
t_diff -= tv2u(&start);
rate = MSG_SZ * MSGS;
rate /= t_diff;
rate *= 1000000;
printf("rate %fM/s\n", rate / (1 << 20));



remain = MSGS;
do write(*sks, msg, sizeof(msg)); while (--remain);

return 0;
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