On Mon, Apr 28, 2014 at 12:18 PM, Srivatsa S. Bhat
<srivatsa.bhat@xxxxxxxxxxxxxxxxxx> wrote:
>
> I hit this during boot on v3.15-rc3, just once so far.
> Subsequent reboots went fine, and a few quick runs of multi-
> threaded ebizzy also didn't recreate the problem.
>
> The kernel I was running was v3.15-rc3 + some totally
> unrelated cpufreq patches.
>
> The BUG_ON triggered from the following code:
>
> 74 struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
> 84 if (vma && vma->vm_start <= addr && vma->vm_end > addr) {
> 85 BUG_ON(vma->vm_mm != mm);
> 86 return vma;
> 87 }
Hmm. Andrew, Davidlohr, I thought we agreed that he non-current mm
case can actually happen, and that the BUG_ON() was wrong and we
should compare the mm pointer. But the patch that got merged obviously
has the BUG_ON(), so my memory must be wrong.
Regardless, I absolutely *detest* random BUG_ON() calls that turn a
debuggability problem totally unnecessarily into a hard failure, so
that BUG_ON() really needs to go away. I *know* I suggested using
WARN_ON_ONCE() when the discussion was about whether the condition
could happen or not, and the fact that it got turned into a BUG_ON()
is a damn shame.
Andrew, I think I blame you for that particular BUG_ON() addition,
because I don't see it in the original patch. There is *no* excuse for
a BUG_ON(), when a
if (WARN_ON_ONCE(vma->vm_mm != mm))
return NULL;
would have worked equally well without killing the box and making
things harder to debug.
This BUG_ON() insanity needs to stop. The thing is a f*cking menace,
and it's not the first time we hit a BUG_ON() that damn well shouldn't
have been a BUG_ON() to begin with.
That said, the bug does seem to be that some path doesn't invalidate
the vmacache sufficiently, or something inserts a vmacache entry into
the current process when looking up a remote process or whatever.
Davidlohr, ideas?
Linus
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