Re: panic with out of memory

On Wed, Jun 20, 2012 at 08:19:39AM -0400, John Baldwin wrote:
> 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)
> _at__at_ -475,12 +475,14 _at__at_ 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
> _at__at_ -494,6 +496,7 _at__at_ vm_map_process_deferred(void)
>  			    entry->end);
>  		}
>  		vm_map_entry_deallocate(entry, FALSE);
> +		entry = next;
>  	}
>  }

Yes, looks like it should work.