Date: Wed, 20 Jun 2012 08:19:39 -0400 From: John Baldwin <jhb@freebsd.org> To: Alan Cox <alc@freebsd.org> Cc: Steve Wills <swills@freebsd.org>, Konstantin Belousov <kib@freebsd.org>, current@freebsd.org Subject: Re: panic with out of memory Message-ID: <201206200819.39256.jhb@freebsd.org> In-Reply-To: <4FE127D3.8070502@FreeBSD.org> References: <4FE127D3.8070502@FreeBSD.org>
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On Tuesday, June 19, 2012 9:30:59 pm Steve Wills wrote:
> Hi,
>
> I just got a panic out of my r237195 system. The panic looks like:
>
> Sleeping thread (tid 173153, pid 42034) owns a non-sleepable lock
> KDB: stack backtrace of thread 173153:
> sched_switch() at sched_switch+0x28a
> mi_switch() at mi_switch+0xdf
> sleepq_timedwait() at sleepq_timedwait+0x3a
> _sleep() at _sleep+0x266
> swp_pager_meta_build() at swp_pager_meta_build+0x259
> swap_pager_copy() at swap_pager_copy+0x17b
> vm_object_collapse() at vm_object_collapse+0x123
> vm_object_deallocate() at vm_object_deallocate+0x457
> vm_map_process_deferred() at vm_map_process_deferred+0x72
> vm_pageout_oom() at vm_pageout_oom+0x180
> swp_pager_meta_build() at swp_pager_meta_build+0x248
> swap_pager_copy() at swap_pager_copy+0x17b
> vm_object_collapse() at vm_object_collapse+0x123
> vm_object_deallocate() at vm_object_deallocate+0x457
> vm_map_process_deferred() at vm_map_process_deferred+0x72
> vm_map_remove() at vm_map_remove+0x116
> exec_new_vmspace() at exec_new_vmspace+0x1bc
> exec_elf64_imgact() at exec_elf64_imgact+0x5f4
> kern_execve() at kern_execve+0x6f0
> sys_execve() at sys_execve+0x37
> amd64_syscall() at amd64_syscall+0x351
> Xfast_syscall() at Xfast_syscall+0xfb
> --- syscall (59, FreeBSD ELF64, sys_execve), rip = 0x800d2eddc, rsp =
> 0x7fffffffd328, rbp = 0x7fffffffd470 ---
> panic: sleeping thread
> cpuid = 4
>
> The system was very busy and using lots of swap, but I didn't expect a
> panic. If any more detail is needed or I should just get more RAM, let
> me know. :)
Hmm, this is due to a bug I noticed recently as well. I had been talking
with Alan and Konstantin about the proper fix. Hmm, thinking abou this some
more, perhaps a simpler fix would be to have a 'I'm already in
vm_map_process_deferred()' flag. Or even better, just move the entire list
off into a static variable so that we don't get caught in recursion.
Something like this:
Index: vm_map.c
===================================================================
--- vm_map.c (revision 237227)
+++ vm_map.c (working copy)
@@ -475,12 +475,14 @@ static void
vm_map_process_deferred(void)
{
struct thread *td;
- vm_map_entry_t entry;
+ vm_map_entry_t entry, next;
vm_object_t object;
td = curthread;
- while ((entry = td->td_map_def_user) != NULL) {
- td->td_map_def_user = entry->next;
+ entry = td->td_map_def_user;
+ td->td_map_def_user = NULL;
+ while (entry != NULL) {
+ next = entry->next;
if ((entry->eflags & MAP_ENTRY_VN_WRITECNT) != 0) {
/*
* Decrement the object's writemappings and
@@ -494,6 +496,7 @@ vm_map_process_deferred(void)
entry->end);
}
vm_map_entry_deallocate(entry, FALSE);
+ entry = next;
}
}
--
John Baldwin
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