Messages in this thread | | | Date | Thu, 12 Jun 2008 20:33:23 +0200 | From | Manfred Spraul <> | Subject | Re: repeatable slab corruption with LTP msgctl08 |
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Pekka J Enberg wrote: > Hi Andrew, > > On Wed, 11 Jun 2008, Andrew Morton wrote: > >> version is ltp-full-20070228 (lots of retro-computing there). >> >> Config is at http://userweb.kernel.org/~akpm/config-vmm.txt >> >> ./testcases/bin/msgctl08 crashes after ten minutes or so: >> >> slab: Internal list corruption detected in cache 'size-128'(26), slabp f2905000(20). Hexdump: >> >> 000: 00 e0 12 f2 88 32 c0 f7 88 00 00 00 88 50 90 f2 >> 010: 14 00 00 00 0f 00 00 00 00 00 00 00 ff ff ff ff >> 020: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff >> 030: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff >> 040: fd ff ff ff fd ff ff ff 00 00 00 00 fd ff ff ff >> 050: fd ff ff ff fd ff ff ff 19 00 00 00 17 00 00 00 >> 060: fd ff ff ff fd ff ff ff 0b 00 00 00 fd ff ff ff >> 070: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff >> 080: 10 00 00 00 >> > > Looking at the above dump, slabp->free is 0x0f and the bufctl it points to > is 0xff ("BUFCTL_END") which marks the last element in the chain. This is > wrong as the total number of objects in the slab (cachep->num) is 26 but > the number of objects in use (slabp->inuse) is 20. So somehow you have > managed to lost 6 objects from the bufctl chain. > > Hmm. double kfree() should be cached by the redzone code. And I disagree with your link interpretation:
000: 00 e0 12 f2 88 32 c0 f7 88 00 00 00 88 50 90 f2 010: inuse: 14 00 00 00 (20 entries in use, 6 should be free) free: 0f 00 00 00 nodeid: 00 00 00 00 bufctl[0x00] ff ff ff ff 020: fd ff ff ff fd ff ff ff fd ff ff ff bufctl[0x4] fd ff ff ff 030: fd ff ff ff fd ff ff ff fd ff ff ff bufctl[0x8] fd ff ff ff 040: fd ff ff ff fd ff ff ff 00 00 00 00 bufctl[0x0c] fd ff ff ff 050: fd ff ff ff fd ff ff ff 19 00 00 00 bufctl[0x10] 17 00 00 00 060: fd ff ff ff fd ff ff ff 0b 00 00 00 bufctl[0x14] fd ff ff ff 070: fd ff ff ff fd ff ff ff fd ff ff ff bufctl[0x18] fd ff ff ff 080: 10 00 00 00
free: points to entry 0x0f. bufctl[0x0f] is 0x19, i.e. it points to entry 0x19 0x19 points to 0x10 0x10 points to 0x17 0x17 is a BUFCTL_ACTIVE - that's a bug. but: 0x13 is a valid link entry, is points to 0x0b 0x0b points to 0x00, which is BUFCTL_END.
IMHO the most probable bug is a single bit error: bufctl[0x10] should be 0x13 instead of 0x17.
What about printing all redzone words? That would allow us to validate the bufctl chain.
Andrew: Could you post the new oops?
-- Manfred
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