[PATCH 4/5] kgdb: Use atomic operators whichuse barriers
in [Kernel]
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From: Will Deacon on 19 Apr 2010 11:30 Hi Jason, > Here is the revised patch, which is going into the kgdb-fixes branch. > > Thanks, > Jason. > > -- > From: Jason Wessel <jason.wessel(a)windriver.com> > Subject: [PATCH] kgdb: Use atomic operators which use barriers > > The cpu_relax() does not mandate that there is an smp memory barrier. > As a result on the arm smp architecture the kernel debugger can hang > on entry from time to time, as shown by the kgdb regression tests. > > The solution is simply to use the atomic operators which include a > proper smp memory barrier, instead of using atomic_set(). > > Tested-by: Will Deacon <will.deacon(a)arm.com> > Signed-off-by: Jason Wessel <jason.wessel(a)windriver.com> > --- > kernel/kgdb.c | 15 +++++++-------- > 1 file changed, 7 insertions(+), 8 deletions(-) > > --- a/kernel/kgdb.c > +++ b/kernel/kgdb.c > @@ -1379,8 +1379,7 @@ acquirelock: > * Make sure the above info reaches the primary CPU before > * our cpu_in_kgdb[] flag setting does: > */ > - smp_wmb(); > - atomic_set(&cpu_in_kgdb[cpu], 1); > + atomic_inc(&cpu_in_kgdb[cpu]); As Dmitry pointed out here: http://lkml.org/lkml/2010/4/8/214 This bit of code looks broken, especially since the comment has been left alone by the patch. I think commit ae6bf53e should be reverted because semantically all it does is remove the smp_wmb() above. Please let me know what you think, Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |