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Date:      Fri, 24 Feb 2006 07:43:21 -0500
From:      John Baldwin <jhb@freebsd.org>
To:        freebsd-sparc64@freebsd.org
Cc:        sparc64@freebsd.org, Kris Kennaway <kris@obsecurity.org>
Subject:   Re: "sched_lock held too long" panic + trace
Message-ID:  <200602240743.22979.jhb@freebsd.org>
In-Reply-To: <20060223230734.GA93088@xor.obsecurity.org>
References:  <20060223204716.GA90985@xor.obsecurity.org> <20060223230734.GA93088@xor.obsecurity.org>

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On Thursday 23 February 2006 06:07 pm, Kris Kennaway wrote:
> On Thu, Feb 23, 2006 at 03:47:16PM -0500, Kris Kennaway wrote:
> > One of my e4500s has started panicking regularly under load because
> > sched_lock was held for > 5 seconds.  Since on sparc64 it always
> > deadlocks after this panic instead of entering DDB, I wasn't able to
> > track down the cause.  Instead, I changed the panic to first
> > DELAY(1000000*PCPU_GET(cpuid)) (so that different CPUs don't overlap
> > the printfs) and then kdb_backtrace().
> >
> > Doing so I obtained the following trace (still a bit corrupted, but
> > hopefully more useful).
> >
> > KDB: stack backtrace:
> > hardclock_cpu() at hardclock_cpu+0x6c
> > tick_hardclock() at tick_hardclock+0xc4
> > -- interrupt level=3D0xe pil=3D0 %o7=3D0xc0190a98 --
> > _mtx_lock_spin() at _mtx_lock_spin+0xf4
> > tlb_page_demap() at tlb_page_demap+0xa0
> > pmap_zero_page_idle() at pmap_zero_page_idle+0xdc
> > vm_page_zero_idle() at vm_page_zero_idle+0x108
> > vm_pagezero() at vm_pagezero+0x4c
> > fork_exit() at fork_exit+0x94
> > fork_trampoline() at fork_trampoline+0x8
>
> Witness seems to have caught this:
>
> panic: blockable sleep lock (sleep mutex) system map @ vm/vm_map.c:2995
> db> wh
> Tracing pid 1267 tid 100248 td 0xfffff800612a0540
> panic() at panic+0x164
> witness_checkorder() at witness_checkorder+0xc8
> _mtx_lock_flags() at _mtx_lock_flags+0x80
> _vm_map_lock_read() at _vm_map_lock_read+0x3c
> vm_map_lookup() at vm_map_lookup+0x1c
> vm_fault() at vm_fault+0x68
> trap_pfault() at trap_pfault+0x1a8
> trap() at trap+0x2b0
> -- fast data access mmu miss tar=3D0xe819c000 %o7=3D0xc031d204 --
> cpu_ipi_selected() at cpu_ipi_selected+0x2c
> tlb_page_demap() at tlb_page_demap+0x74
> pmap_copy_page() at pmap_copy_page+0x39c
> vm_fault() at vm_fault+0xe5c
> trap_pfault() at trap_pfault+0x134
> trap() at trap+0xa0
> -- data access protection tar=3D0x4065c524 sfar=3D0x4065d314 sfsr=3D0x800=
005
> %o7=3D0x40350c94 --

This is just a bug.  You shouldn't get a pagefault in cpu_ipi_selected().

=2D-=20
John Baldwin <jhb@FreeBSD.org> =A0<>< =A0http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" =A0=3D =A0http://www.FreeBSD.org



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