Re: WARNING: at mm/slub.c:3357, kernel BUG at mm/slub.c:3413

[Markus Trippelsdorf <markus@trippelsdorf.de>]

On 2011.11.22 at 10:38 +0100, Eric Dumazet wrote:
> Le mardi 22 novembre 2011 a 09:45 +0100, Markus Trippelsdorf a ecrit :
> 
> > I sometimes see the following pattern. Is this a false positive?
> > 
> > 
> > =============================================================================
> > BUG anon_vma: Redzone overwritten
> > -----------------------------------------------------------------------------
> > 
> > INFO: 0xffff88020f347c80-0xffff88020f347c87. First byte 0xbb instead of 0xcc
> > INFO: Allocated in anon_vma_fork+0x51/0x140 age=1 cpu=2 pid=1826
> > 	__slab_alloc.constprop.70+0x1ac/0x1e8
> > 	kmem_cache_alloc+0x12e/0x160
> > 	anon_vma_fork+0x51/0x140
> > 	dup_mm+0x1f2/0x4a0
> > 	copy_process+0xd10/0xf70
> > 	do_fork+0x100/0x2b0
> > 	sys_clone+0x23/0x30
> > 	stub_clone+0x13/0x20
> > INFO: Freed in __put_anon_vma+0x54/0xa0 age=0 cpu=1 pid=1827
> > 	__slab_free+0x33/0x2d0
> > 	kmem_cache_free+0x10e/0x120
> > 	__put_anon_vma+0x54/0xa0
> > 	unlink_anon_vmas+0x12f/0x1c0
> > 	free_pgtables+0x83/0xe0
> > 	exit_mmap+0xee/0x140
> > 	mmput+0x43/0xf0
> > 	flush_old_exec+0x33f/0x630
> > 	load_elf_binary+0x340/0x1960
> > 	search_binary_handler+0x8f/0x180
> > 	do_execve+0x2d3/0x370
> > 	sys_execve+0x42/0x70
> > 	stub_execve+0x6c/0xc0
> > INFO: Slab 0xffffea00083cd1c0 objects=10 used=9 fp=0xffff88020f347ab8 flags=0x4000000000000081
> > INFO: Object 0xffff88020f347c40 @offset=3136 fp=0xffff88020f347ab8
> > 
> > Bytes b4 ffff88020f347c30: 39 b6 fb ff 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a  9.......ZZZZZZZZ
> > Object ffff88020f347c40: 30 c9 9b 0d 02 88 ff ff 01 00 00 00 00 00 5a 5a  0.............ZZ
> > Object ffff88020f347c50: 50 7c 34 0f 02 88 ff ff 50 7c 34 0f 02 88 ff ff  P|4.....P|4.....
> > Object ffff88020f347c60: 00 00 00 00 00 00 00 00 00 00 00 00 5a 5a 5a 5a  ............ZZZZ
> > Object ffff88020f347c70: 70 7c 34 0f 02 88 ff ff 70 7c 34 0f 02 88 ff ff  p|4.....p|4.....
> > Redzone ffff88020f347c80: bb bb bb bb bb bb bb bb                          ........
> > Padding ffff88020f347dc0: 5a 5a 5a 5a 5a 5a 5a 5a                          ZZZZZZZZ
> > Pid: 1820, comm: slabinfo Not tainted 3.2.0-rc2-00369-gbbbc479-dirty #83
> > Call Trace:
> >  [<ffffffff81105df8>] ? print_section+0x38/0x40
> >  [<ffffffff811062f3>] print_trailer+0xe3/0x150
> >  [<ffffffff811064f0>] check_bytes_and_report+0xe0/0x100
> >  [<ffffffff81107313>] check_object+0x183/0x240
> >  [<ffffffff81107eb0>] validate_slab_slab+0x1c0/0x230
> >  [<ffffffff8110a4a6>] validate_store+0xa6/0x190
> >  [<ffffffff8110573c>] slab_attr_store+0x1c/0x30
> >  [<ffffffff81168838>] sysfs_write_file+0xc8/0x140
> >  [<ffffffff811124a3>] vfs_write+0xa3/0x160
> >  [<ffffffff81112635>] sys_write+0x45/0x90
> >  [<ffffffff814d3ffb>] system_call_fastpath+0x16/0x1b
> > FIX anon_vma: Restoring 0xffff88020f347c80-0xffff88020f347c87=0xcc
> 
> 
> Wait a minute
> 
> You trigger this using slabinfo looping or something ?
> 
> Bug is in slabinfo then, dont use it, and see if bug triggers.
> 
> Given slub is now lockless, validate_slab_slab() is probably very wrong
> these days.

OK "slabinfo -v" is useless then. But that doesn't invalidate the BUGs
that I saw during boot. They happend before I could even run slabinfo
for the first time.

-- 
Markus

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