Date: Mon, 23 Jun 2008 13:16:40 -0600 From: James Gritton <jamie@gritton.org> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-hackers@freebsd.org, freebsd-stable@freebsd.org Subject: Re: FreeBSD 6.3 deadlock (vm_map?) with DDB output Message-ID: <485FF698.103@gritton.org> In-Reply-To: <200806231451.52340.jhb@freebsd.org> References: <20080615112318.146C1F18512@mx.npubs.com> <200806180917.05689.jhb@freebsd.org> <485A81FF.1000000@gritton.org> <200806231451.52340.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
John Baldwin wrote: > On Thursday 19 June 2008 11:57:51 am James Gritton wrote: > >> 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? >> > > If people confirm it fixes issues I will MFC it. There was some pushback when > I first committed it so I waited on the MFC. I can confirm that on 6.3 I can recreate the deadlock without the patch, and can't recreate it with the patch.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?485FF698.103>