Messages in this thread |  | | From | Neil Brown <> | Date | Wed, 7 Feb 2007 06:45:41 +1100 | Subject | Re: Could "bio_vec" be referenced any time? |
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On Tuesday February 6, g944370@oz.nthu.edu.tw wrote: > Hi all, > I write a module that creates a kernel thread to show the BIOs from > MD modules. > The kernel thread will call show_bio() when md passing a BIO to my > module,else sleep. > Sometimes, show_bio() continues working successfully ,but it > somtimes makes "general protection fault". > The show_bio() always works when I comment the > "bio_for_each_segment" loop. > Is the zone I comment the cause of the fault? > As above, I consider it's the main problem.Also, I strongly want to > know your opinions.Thank you for help. > > THX
Without seeing how the bio gets to show_bio it is hard to be certain, but my guess would be that by the time show_bio tries to inspect the bio, the IO request involving it has already completed and the bio has been freed, so you are accessing freed memory.
> Feb 6 22:00:28 RAID-SUSE kernel: Code: 8b 00 f6 c4 08 74 0e 48 c7 c7 14 9c > 45 88 31 c0 e8 b5 bf e2
If you feed this line into ksymoops you get:
Code; 0000000000000000 Before first symbol 0: 8b 00 mov (%rax),%eaxC ...
so it is trying to dereference $rax.
> Feb 6 22:00:28 RAID-SUSE kernel: RAX: 6b6b6b6b6b6b6b6b RBX: > ffff810037f52668 RCX: 0000000000040000
Which contains 6b6b6b6b6b6b6b6b. which is lots of copies of 'POISON_FREE' (defined in include/linux/poison.h) which makes it really look like that memory has already been freed.
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