'make -j16 universe' gives SIReset

[Marius Strobl]

On Sat, Jul 02, 2011 at 02:03:41PM -0500, Alan Cox wrote:
> On 07/01/2011 19:23, Marius Strobl wrote:
> >On Fri, Jul 01, 2011 at 08:17:52AM +1000, Peter Jeremy wrote:
> >>[Moving back on-list]
> >>
> >>On 2011-Jun-30 06:30:08 +0800, Marius Strobl<marius at alchemy.franken.de>  
> >>wrote:
> >>>On Thu, Jun 30, 2011 at 08:00:10AM +1000, Peter Jeremy wrote:
> >>>>On 2011-Jun-29 19:54:44 +0200, Marius Strobl<marius at alchemy.franken.de> 
> >>>>wrote:
> >>>>>On Wed, Jun 29, 2011 at 12:54:33PM +1000, Peter Jeremy wrote:
> >>>>>>My V890 has been running "make -j32 buildworld" in a loop for a
> >>>>>>week now without problems so I think that was the problem.
> >>>>OTOH, a V440 that has been running similar load for a similar period
> >>>>died overnight with:
> >>>>
> >>>>panic: uma_small_alloc: free page still has mappings!
> >>>>VNASSERT failed
> >>>>cpuid = 3
> >>>>0xfffff800079643c0: KDB: enter: panic
> >>...
> >>>>I'm fairly sure that is the same kernel but will double-check and
> >>>>investigate that panic further.
> >>FWIW, that kernel didn't have the latest patchset (adding Zeus support).
> >That shouldn't make a difference; the later version only adds the
> >SPARC64 bits as you already noticed and adjusts the boot loader to
> >compile again. I made no changes to the existing parts apart from
> >fixing a comment. Besides I see no connection between fixing the
> >gross user TLB flushing and the below problem so far.
> >
> >>>Ok, this appears to be an unrelated problem though. Alan, do you
> >>>have an idea what could be causing this?
> >>I managed to get the same panic (though different traceback) on the
> >>V890 after about an hour of pho@'s stress test with INCARNATIONS=150:
> >>
> >>panic: uma_small_alloc: free page still has mappings!
> >>cpuid = 1
> >>KDB: enter: panic
> >>[ thread pid 142 tid 100196 ]
> >>Stopped at      kdb_enter+0x80: ta              %xcc, 1
> >>db>  where
> >>Tracing pid 142 tid 100196 td 0xfffff8a016ace880
> >>panic() at panic+0x20c
> >>uma_small_alloc() at uma_small_alloc+0xe8
> >>keg_alloc_slab() at keg_alloc_slab+0xc8
> >>keg_fetch_slab() at keg_fetch_slab+0x218
> >>zone_fetch_slab() at zone_fetch_slab+0x44
> >>uma_zalloc_arg() at uma_zalloc_arg+0x60c
> >>m_getm2() at m_getm2+0x134
> >>m_uiotombuf() at m_uiotombuf+0x4c
> >>sosend_generic() at sosend_generic+0x420
> >>sosend() at sosend+0x2c
> >>soo_write() at soo_write+0x3c
> >>dofilewrite() at dofilewrite+0x7c
> >>kern_writev() at kern_writev+0x38
> >>write() at write+0x4c
> >>syscallenter() at syscallenter+0x270
> >>syscall() at syscall+0x74
> >>-- syscall (4, FreeBSD ELF64, write) %o7=0x101db4 --
> >>userland() at 0x405936c8
> >>user trace: trap %o7=0x101db4
> >>pc 0x405936c8, sp 0x7fdffffd8a1
> >>pc 0x101f44, sp 0x7fdffffd9a1
> >>pc 0x104604, sp 0x7fdffffda81
> >>pc 0x1046f0, sp 0x7fdffffdb51
> >>pc 0x104994, sp 0x7fdffffdc21
> >>pc 0x104d90, sp 0x7fdffffdd01
> >>pc 0x101610, sp 0x7fdffffde41
> >>pc 0x4020cff4, sp 0x7fdffffdf01
> >>done
> >>db>
> >>
> >>I've got a crashdump on the V440 but discovered that gdb reports
> >>"GDB can't read core files on this machine." so it isn't much use.
> >>Any suggestions on how to debug this?
> >The VM and its interaction with the MD code are beyond me, I hope
> >Alan can chime in here. Reading through the code I see a possible
> >path which could lead to this though; tsb_tte_enter(), which is
> >the only place where TD_PV ever is set and also only in case of
> >managed pages, always calls pmap_cache_enter(), which together
> >with pmap_cache_remove() does the page color handling. In
> >pmap_remove_all() however, pmap_cache_remove() is only called for
> >managed pages, so for unmanaged pages we might miss the removal
> >of the mapping from the the color used. I've no idea though if
> >this actually is relevant, i.e. whether the VM ever calls
> >pmap_remove_all() for unmanaged pages.
> 
> In HEAD, it does not.  Other architectures have an assertion forbidding 
> pmap_remove_all() calls on unmanaged pages.  (Btw, I'm happy to add this 
> assertion to sparc64's pmap if you like.)  In older versions, calling 
> pmap_remove_all() on unmanaged pages is expected to be a harmless NOP 
> that's just a waste of cycles.
> 
> With unmanaged pages, it is expected that pmap_remove() is used to 
> destroy mappings before the page is freed.
> 
> For years, vm_page_free{,_toq}() has asserted that the page has no 
> managed mappings:
> 
>         if ((m->flags & PG_UNMANAGED) == 0) {
>                 vm_page_lock_assert(m, MA_OWNED);
>                 KASSERT(!pmap_page_is_mapped(m),
>                     ("vm_page_free_toq: freeing mapped page %p", m));
>         }
> 

Okay, then my theories don't hold.

> As a debugging aid, you might want to add an additional check here on 
> colors.

I did that and it turns out to trigger rather quickly:
Trying to mount root from nfs: []...
NFS ROOT: 192.168.1.40:/usr/data/nfsroot/sparc64
dc1: link state changed to UP
panic: vm_page_free_toq: free page 0xfffff80047b8a088 still has mappings!
cpuid = 0
KDB: enter: panic
[ thread pid 1 tid 100001 ]
Stopped at      kdb_enter+0x80: ta              %xcc, 1
db> bt
Tracing pid 1 tid 100001 td 0xfffff80041094000
panic() at panic+0x20c
vm_page_free_toq() at vm_page_free_toq+0xb4
vm_page_free_zero() at vm_page_free_zero+0x10
pmap_release() at pmap_release+0x170
vmspace_free() at vmspace_free+0x70
vmspace_exec() at vmspace_exec+0x48
exec_new_vmspace() at exec_new_vmspace+0x240
exec_elf64_imgact() at exec_elf64_imgact+0x598
kern_execve() at kern_execve+0x398
execve() at execve+0x34
start_init() at start_init+0x2ec
fork_exit() at fork_exit+0x9c
fork_trampoline() at fork_trampoline+0x8
db>

Further debugging shows that the page in question is one of the TSB
pages entered by pmap_pinit(). In pmap_release() vm_page_free_zero()
is called on these before pmap_qremove(), so there appears to be a
race in which these pages can get re-used before their mappings are
removed. I suspect that this might be related to your change in
r207648, but just reverting that one nowadays this triggers the
assertion in vm_page_free_toq() about the page lock not being held.
Anyway, I'm not sure what the right fix for this is; should
pmap_release() call pmap_qremove() on these pages one-by-one before
calling vm_page_free_zero() or maybe just call pmap_qremove() for
all of them before looping over them and calling vm_page_free_zero()?

Marius