CUREENT issue with ballon.c

[Konstantin Belousov]

On Thu, Oct 24, 2013 at 09:45:20PM +0100, Roger Pau Monn? wrote:
> On 24/10/13 13:01, Outback Dingo wrote:
> > 
> > 
> > On Thu, Oct 24, 2013 at 6:16 AM, Roger Pau Monn? <roger.pau at citrix.com
> > <mailto:roger.pau at citrix.com>> wrote:
> > 
> >     On 24/10/13 03:02, Outback Dingo wrote:
> >     > --- trap 0, rip = 0, rsp = 0xfffffe00002c6b70, rbp = 0 ---
> >     > uma_zalloc_arg: zone "16" with the following non-sleepable locks held:
> >     > exclusive sleep mutex balloon_lock (balloon_lock) r = 0
> >     > (0xffffffff816e9c58) locked @
> >     /usr/src/sys/dev/xen/balloon/balloon.c:339
> >     > exclusive sleep mutex balloon_mutex (balloon_mutex) r = 0
> >     > (0xffffffff816e9c38) locked @
> >     /usr/src/sys/dev/xen/balloon/balloon.c:373
> >     > KDB: stack backtrace:
> >     > db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame
> >     > 0xfffffe00002c67c0
> >     > kdb_backtrace() at kdb_backtrace+0x39/frame 0xfffffe00002c6870
> >     > witness_warn() at witness_warn+0x4a8/frame 0xfffffe00002c6930
> >     > uma_zalloc_arg() at uma_zalloc_arg+0x3b/frame 0xfffffe00002c69a0
> >     > malloc() at malloc+0x101/frame 0xfffffe00002c69f0
> >     > balloon_process() at balloon_process+0x44a/frame 0xfffffe00002c6a70
> >     > fork_exit() at fork_exit+0x84/frame 0xfffffe00002c6ab0
> >     > fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe00002c6ab0
> >     > --- trap 0, rip = 0, rsp = 0xfffffe00002c6b70, rbp = 0 ---
> >     > uma_zalloc_arg: zone "16" with the following non-sleepable locks held:
> >     > exclusive sleep mutex balloon_lock (balloon_lock) r = 0
> >     > (0xffffffff816e9c58) locked @
> >     /usr/src/sys/dev/xen/balloon/balloon.c:339
> >     > exclusive sleep mutex balloon_mutex (balloon_mutex) r = 0
> >     > (0xffffffff816e9c38) locked @
> >     /usr/src/sys/dev/xen/balloon/balloon.c:373
> >     > KDB: stack backtrace:
> >     > db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame
> >     > 0xfffffe00002c67c0
> >     > kdb_backtrace() at kdb_backtrace+0x39/frame 0xfffffe00002c6870
> >     > witness_warn() at witness_warn+0x4a8/frame 0xfffffe00002c6930
> >     > uma_zalloc_arg() at uma_zalloc_arg+0x3b/frame 0xfffffe00002c69a0
> >     > malloc() at malloc+0x101/frame 0xfffffe00002c69f0
> >     > balloon_process() at balloon_process+0x44a/frame 0xfffffe00002c6a70
> >     > fork_exit() at fork_exit+0x84/frame 0xfffffe00002c6ab0
> >     > fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe00002c6ab0
> >     > --- trap 0, rip = 0, rsp = 0xfffffe00002c6b70, rbp = 0 ---
> >     > uma_zalloc_arg: zone "16" with the following non-sleepable locks held:
> > 
> >     Did you do anything specific to trigger the crash? Can you explain the
> >     steps needed to reproduce it?
> > 
> > 
> > just recompiled a kernel, and booted it scrolls continuously across the
> > screen
> > doesnt seem to ever stop. 
> 
> I've tried r257051 and it seems to work fine, could you please post your
> Xen version, the config file used to launch the VM and the toolstack used?

Do you have witness enabled in your kernel config ?

There is an obvious case of calling malloc(M_WAITOK) while holding both
balloon_lock and balloon_mutex:
ballon_process->decrease_reservation->balloon_append.
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