test9-pre3+t9p2-vmpatch VM deadlock during socket I/O

[Yuri Pudgorodsky <yur@asplinux.ru>]

I also encounter instant lockup of test9-pre3 + t9p2-vmpatch / SMP (two CPU).
under high I/O via UNIX domain sockets:

    - running 10 simple tasks doing
    #define BUFFERSIZE 204800
    for (j = 0; ; j++) {
                        if (socketpair(PF_LOCAL, SOCK_STREAM, 0, p) == -1) {
                                exit(1);
                        }
                        fcntl(p[0], F_SETFL, O_NONBLOCK);
                        fcntl(p[1], F_SETFL, O_NONBLOCK);
                        write(p[0], crap, BUFFERSIZE);
                        write(p[1], crap, BUFFERSIZE);
        }

So it looks like swap_out() cannot obtain lock_kernel()
holded by a swap_out() on a second CPU.... See below.

Call trace (looks very similar on both CPU):

Trace; c020aa3e <stext_lock+18a6/8848>
    (called from c0133eb4 <swap_out+0x28>)
Trace; c0133eb4 <swap_out+28/228>               args (6, 3, 0)
Trace; c0134e50 <refill_inactive+c8/170>        args (3, 1)
Trace; c0134f75 <do_try_to_free_pages+7d/9c>    args (3,1)
Trace; c0135168 <wakeup_kswapd+84/bc>
Trace; c0135d72 <__alloc_pages+1d6/264>
Trace; c0135e17 <__get_free_pages+17/28>
Trace; c01322ce <kmem_cache_grow+e2/264>
....

Under lockup, memory map looks like:

Active: 121 Inactive_dirty: 12217 Inactive_clean: 0 free: 12210 (256 512 768)

and does not change from time to time.

Most frequent EIP locations (from Sys-AltRq/P):

Trace; c0133f74 <swap_out+e8/228>
Trace; c0133f23 <swap_out+97/228>
Trace; c0134039 <swap_out+1ad/228>
Trace; c020aa37 <stext_lock+189f/8848>
Trace; c020aa3e <stext_lock+18a6/8848>


In a hope for a quick fix,
Yuri Pudgorodsky


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