[Unionfs] repeatable kernel BUG in unionfs 2.1.3

[Shaya Potter]

what I'm basically doing is
setup union
while [ 1 ]
	chroot union apt-get install package_$i
	remount add new top branch
	remount mode->ro old top branch

I'm rerunning it w/ a "sync; sync; sync" b/w the chroot and the first 
remount and haven't hit the BUG() yet.

Shaya Potter wrote:
> Just compiled unionfs into 2.6.22.6 and have a repeatable BUG() in a 
> stress test of mine that unionfs seems to tickle.
> 
> My unionfs is slightly modified to allow up to 512 branches (simple 
> header define change).  In this case, I was up to 85 branches when this 
> occured.
> 
> here's the backtrace
> 
> ------------[ cut here ]------------
> Kernel BUG at c0179fea [verbose debug info unavailable]
> invalid opcode: 0000 [#1]
> SMP
> Modules linked in: nfsd exportfs lockd sunrpc af_packet dm_snapshot 
> dm_mirror dm_mod sg sr_mod sd_mod scsi_mod ide_generic ide_cd cdrom 
> i2c_piix4 psmouse i2c_core rtc ext3 jbd mbcache ide_disk serverworks tg3 
> ide_core unix
> CPU:    0
> EIP:    0060:[<c0179fea>]    Not tainted VLI
> EFLAGS: 00010202   (2.6.22.6 #2)
> EIP is at __block_write_full_page+0x179/0x358
> eax: 8000183d   ebx: eb45a208   ecx: 00000014   edx: c1d7c940
> esi: dfcebf60   edi: 00000000   ebp: ebbe748c   esp: dfcebd38
> ds: 007b   es: 007b   fs: 00d8  gs: 0000  ss: 0068
> Process pdflush (pid: 81, ti=dfcea000 task=dfc84a50 task.ti=dfcea000)
> Stack: dfcebd5c c011542e 00000000 00000000 00000000 00001000 eb45a208 
> 00000bff
>        00000000 c014942e f88dd168 c1d7c940 00c00000 00000000 dfcebf60 
> 00000000
>        c017b7b7 dfcebf60 ebbe748c dfcebf60 f88dd168 c1d7c940 c1d7c940 
> eb45a208
> Call Trace:
>  [<c011542e>] __wake_up+0x38/0x4e
>  [<c014942e>] set_page_address+0xa2/0x15c
>  [<f88dd168>] ext3_get_block+0x0/0xd7 [ext3]
>  [<c017b7b7>] block_write_full_page+0xe3/0xee
>  [<f88dd168>] ext3_get_block+0x0/0xd7 [ext3]
>  [<f88ddb79>] ext3_ordered_writepage+0xb5/0x16c [ext3]
>  [<f88ddaa4>] bget_one+0x0/0x7 [ext3]
>  [<f88ddac4>] ext3_ordered_writepage+0x0/0x16c [ext3]
>  [<c01a2765>] unionfs_writepage+0xd9/0x227
>  [<c01445e7>] __writepage+0x8/0x21
>  [<c01444e5>] write_cache_pages+0x1c5/0x2bf
>  [<c01445df>] __writepage+0x0/0x21
>  [<c014462b>] generic_writepages+0x2b/0x2d
>  [<c014466a>] do_writepages+0x3d/0x43
>  [<c017572e>] __sync_single_inode+0x55/0x1bd
>  [<c01758dd>] __writeback_single_inode+0x47/0x1a5
>  [<c0114888>] load_balance_newidle+0x62/0x152
>  [<c0175bc5>] sync_sb_inodes+0x18a/0x268
>  [<c0175d42>] writeback_inodes+0x9f/0xa8
>  [<c01440e3>] background_writeout+0x67/0xa1
>  [<c0144bd3>] __pdflush+0xcb/0x17d
>  [<c0144c85>] pdflush+0x0/0x2c
>  [<c0144c85>] pdflush+0x0/0x2c
>  [<c0144cad>] pdflush+0x28/0x2c
>  [<c014407c>] background_writeout+0x0/0xa1
>  [<c012b2a6>] kthread+0x6b/0x6f
>  [<c012b23b>] kthread+0x0/0x6f
>  [<c010339b>] kernel_thread_helper+0x7/0x10
>  =======================
> Code: 5b 5e 5f 5d c3 8b 44 24 2c e8 d0 4d fc ff 8b 4c 24 44 83 41 10 01 
> eb e1 89 da b8 01 00 00 00 e8 8d 18 00 00 83 44 24 10 01 eb ad <0f> 0b 
> eb fe 8b 74 24 44 8b 7e 04 85 ff 75 06 f6 46 24 01 75 37
> EIP: [<c0179fea>] __block_write_full_page+0x179/0x358 SS:ESP 0068:dfcebd38
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