On Sun, Jan 13, 2013 at 7:05 PM, Eric Dumazet <[email protected]> wrote:
> Oh well yes, this doesnt quite work on !SMP. > Strange - how would one assert a spin lock is held, and obviously only for SMP? (I almost think arch_spin_is_locked(lock) should be ((void)(lock), 1) for UP for the purpose of assertion...) Also it looks like there are bunch of other places spin_is_locked() assertion is made in the source tree. (Perhaps they are only configured for MP?) Thanks, Jerry > And this kind of bug is frequent.... > > See following example : > > commit b9980cdcf2524c5fe15d8cbae9c97b3ed6385563 > Author: Hugh Dickins <[email protected]> > Date: Wed Feb 8 17:13:40 2012 -0800 > > mm: fix UP THP spin_is_locked BUGs > > Fix CONFIG_TRANSPARENT_HUGEPAGE=y CONFIG_SMP=n CONFIG_DEBUG_VM=y > CONFIG_DEBUG_SPINLOCK=n kernel: spin_is_locked() is then always false, > and so triggers some BUGs in Transparent HugePage codepaths. > > asm-generic/bug.h mentions this problem, and provides a WARN_ON_SMP(x); > but being too lazy to add VM_BUG_ON_SMP, BUG_ON_SMP, WARN_ON_SMP_ONCE, > VM_WARN_ON_SMP_ONCE, just test NR_CPUS != 1 in the existing VM_BUG_ONs. > > Signed-off-by: Hugh Dickins <[email protected]> > Cc: Andrea Arcangeli <[email protected]> > Cc: <[email protected]> > Signed-off-by: Andrew Morton <[email protected]> > Signed-off-by: Linus Torvalds <[email protected]> > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index b3ffc21..91d3efb 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2083,7 +2083,7 @@ static void collect_mm_slot(struct mm_slot *mm_slot) > { > struct mm_struct *mm = mm_slot->mm; > > - VM_BUG_ON(!spin_is_locked(&khugepaged_mm_lock)); > + VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock)); > > > > > On Sun, Jan 13, 2013 at 1:39 PM, Felix Fietkau <[email protected]> wrote: > >> On 2013-01-13 7:03 PM, Eric Dumazet wrote: >> > I suspect a bug in the spin_is_locked() implementation on your arch, as >> > he socket lock should be held at this point. >> I don't think this is an arch implementation bug, this probably happens >> on all !SMP systems. See this bit from include/linux/spinlock_up.h: >> >> #define arch_spin_is_locked(lock) ((void)(lock), 0) >> >> - Felix >> >> >
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