Messages in this thread | | | Subject | Re: bio linked list corruption. | From | Andy Lutomirski <> | Date | Tue, 18 Oct 2016 18:05:57 -0700 |
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On 10/18/2016 05:10 PM, Linus Torvalds wrote: > On Tue, Oct 18, 2016 at 4:42 PM, Chris Mason <clm@fb.com> wrote: >> >> Seems to be the whole thing: > > Ahh. On lkml, so I do have it in my mailbox, but Dave changed the > subject line when he tested on ext4 rather than btrfs.. > > Anyway, the corrupted address is somewhat interesting. As Dave Jones > said, he saw > > list_add corruption. prev->next should be next (ffffe8ffff806648), > but was ffffc9000067fcd8. (prev=ffff880503878b80). > list_add corruption. prev->next should be next (ffffe8ffffc05648), > but was ffffc9000028bcd8. (prev=ffff880503a145c0). > > and Dave Chinner reports > > list_add corruption. prev->next should be next (ffffe8ffffc02808), > but was ffffc90005f6bda8. (prev=ffff88013363bb80). > > and it's worth noting that the "but was" is a remarkably consistent > vmalloc address (the ffffc9000.. pattern gives it away). In fact, it's > identical across two boots for DaveJ in the low 14 bits, and fairly > high up in those low 14 bots (0x3cd8). > > DaveC has a different address, but it's also in the vmalloc space, and > also looks like it is fairly high up in 14 bits (0x3da8). So in both > cases it's almost certainly a stack address with a fairly empty stack. > The differences are presumably due to different kernel configurations > and/or just different filesystems calling the same function that does > the same bad thing but now at different depths in the stack. > > Adding Andy to the cc, because this *might* be triggered by the > vmalloc stack code itself. Maybe the re-use of stacks showing some > problem? Maybe Chris (who can't see the problem) doesn't have > CONFIG_VMAP_STACK enabled?
Wouldn't this cause the exact opposite problem? If the warning is to be believed, then prev is *not* on the stack but somehow prev->next ended up pointing to the stack. If stack reuse caused something to corrupt a value on the stack, then how would this cause a stack address to be written to a non-stack location? All I can think of is that "prev" itself is corrupted somehow.
One possible debugging approach would be to change:
#define NR_CACHED_STACKS 2
to
#define NR_CACHED_STACKS 0
in kernel/fork.c and to set CONFIG_DEBUG_PAGEALLOC=y. The latter will force an immediate TLB flush after vfree.
Also, CONFIG_DEBUG_VIRTUAL=y can be quite helpful for debugging stack issues. I'm tempted to do something equivalent to hardwiring that option on for a while if CONFIG_VMAP_STACK=y.
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