FreeBSD 6.3 deadlock (vm_map?) with DDB output
James Gritton
jamie at gritton.org
Thu Jun 19 16:18:34 UTC 2008
John Baldwin wrote:
> On Sunday 15 June 2008 07:23:19 am Stef Walter wrote:
>
>> I've been trying to track down a deadlock on some newish production
>> servers running FreeBSD 6.3-RELEASE-p2. The deadlock occurs on a
>> specific (although mundane) hardware configuration, and each of several
>> servers running this hardware deadlock about once per week.
>>
>> Although I suspect that this is not hardware related, from a (naive)
>> perusal of the attached stack traces.
>>
>> Forgive me if my interpretation of this is all wrong, but I'm pretty
>> desperate for help. So here's my basic understanding of the deadlock:
>>
>> These processes seem to be waiting on the page queue mutex:
>> sendmail (in vm_mmap > vm_map_find > vm_map_insert > vm_map_pmap_enter)
>> bsnmpd (in malloc, uma_large_malloc > page_alloc > kmem_malloc)
>> httpd (in trap > trap_pfault > vm_fault)
>> [g_up] (in g_vfs_done > bufdone)
>>
>> The page queue mutex is held by rsync process:
>> rsync (in trap > trap_pfault > vm_fault > pmap_enter)
>>
>> Rsync kernel process (in pmap_enter) was interrupted while holding the
>> page queue lock?
>>
>>
>> Giant is enabled in loader.conf due to the needs of the pf firewall when
>> dealing with user credentials lookups. I do not believe that Giant plays
>> into this deadlock. Kernel config attached.
>>
>> Any and all help or info is welcome. Thanks in advance.
>>
>
> Try this change:
>
> jhb 2007-10-27 22:07:40 UTC
>
> FreeBSD src repository
>
> Modified files:
> sys/kern sched_4bsd.c
> Log:
> Change the roundrobin implementation in the 4BSD scheduler to trigger a
> userland preemption directly from hardclock() via sched_clock() when a
> thread uses up a full quantum instead of using a periodic timeout to cause
> a userland preemption every so often. This fixes a potential deadlock
> when IPI_PREEMPTION isn't enabled where softclock blocks on a lock held
> by a thread pinned or bound to another CPU. The current thread on that
> CPU will never be preempted while softclock is blocked.
>
> Note that ULE already drives its round-robin userland preemption from
> sched_clock() as well and always enables IPI_PREEMPT.
>
> MFC after: 1 week
>
> Revision Changes Path
> 1.108 +8 -29 src/sys/kern/sched_4bsd.c
>
> We use it at work on 6.x. W/o this fix, round-robin stops working on 4BSD
> when softclock() (swi4: clock) blocks on a lock like Giant.
>
I've been seeing similar troubles on 6.2 and I'll have to give this a
try as we upgrade to 6.3. I notice "MFC after: 1 week" in the log; it's
been a week - any chance of seeing this fix rolled into 6.x?
- Jamie
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