Re: CVS commit: src/sys/netinet

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

On Tue, Dec 26, 2017 at 5:23 PM, Ryota Ozaki <ozaki-r%netbsd.org@localhost> wrote:
> On Tue, Dec 26, 2017 at 4:50 PM, Tom Ivar Helbekkmo
> <tih%hamartun.priv.no@localhost> wrote:
>> Ryota Ozaki <ozaki-r%NetBSD.org@localhost> writes:
>>
>>> One possible fix has been committed.
>>>
>>> Can you update the source code and try a new kernel?
>>
>> Will do.
>
> Thanks.
>
>
>>
>> Meanwhile, before I got around to building a kernel with debug options
>> enabled, I had another hang.  Got it into DDB successfully, but then I
>> managed, while looking for a way to switch between CPUs (the man page is
>> wrong in this respect), to get DDB to look at something it shouldn't
>> have, so it just said "fatal pag", and that was that.
>>
>> I did get a backtrace of CPU 0, though, and it looked interesting:
>>
>> pool_catchup()
>> pool_get()
>> pool_cache_get_slow()
>> pool_cache_get_paddr()
>> m_get()
>> m_gethdr()
>> wm_add_rxbuf()
>> wm_rxeof()
>> wm_intr_legacy()
>> intr_biglock_wrapper()
>> Xintr_ioapic_level2()
>> --- interrupt ---
>> Xspllower()
>> uvm_km_kmem_alloc()
>> pool_page_alloc()
>> pool_grow()
>> pool_catchup()
>> pool_get()
>> pool_cache_get_slow()
>> pool_cache_get_paddr()
>> m_get()
>> m_gethdr()
>> tcp_output()
>> tcp_send_wrapper()
>> sosend()
>> soo_write()
>> dofilewrite()
>> sys_write()
>> syscall()
>> --- syscall (number 4) ---
>
> Looks the below infinite loop is happening?
>
> I think we need to summon a pool expert.
>
>   ozaki-r
>
>
> (Copied and modified the diagram from PR 52858)
>
>  [lwp #1]
>     |
>  [pool_grow with PR_NOWAIT
>  [set PR_GROWING and PR_GROWINGNOWAIT
>  [mutex_exit(&pp->pr_lock)
>     |
>  (interrupted)
>
>  [intr #1]
>     |
>  [pool_catchup
>  [pool_grow with PR_NOWAIT
>  [see PR_GROWING and PR_GROWINGNOWAIT are set
>  [return ERESTART
>  [repeat pool_grow in pool_catchup...

I think the below patch fixes the above issue, but probably
there is a better solution.

  ozaki-r

diff --git a/sys/kern/subr_pool.c b/sys/kern/subr_pool.c
index 3e6c9225482..e4be8bf0682 100644
--- a/sys/kern/subr_pool.c
+++ b/sys/kern/subr_pool.c
@@ -1247,6 +1247,7 @@ static int
 pool_catchup(struct pool *pp)
 {
        int error = 0;
+       int s = splvm();

        while (POOL_NEEDS_CATCHUP(pp)) {
                error = pool_grow(pp, PR_NOWAIT);
@@ -1256,6 +1257,7 @@ pool_catchup(struct pool *pp)
                        break;
                }
        }
+       splx(s);
        return error;
 }