Re: [tip:perf/core] x86, mm, perf: Allow recursive faults from interrupts

[Waiman Long]

On 01/17/2014 02:17 PM, Andy Lutomirski wrote:
> On Fri, Jan 17, 2014 at 10:10 AM, Waiman Long<waiman.long@xxxxxx>  wrote:
> > On 01/16/2014 08:39 AM, tip-bot for Peter Zijlstra wrote:
> > > Commit-ID:  c026b3591e4f2a4993df773183704bb31634e0bd
> > > Gitweb:
> > > http://git.kernel.org/tip/c026b3591e4f2a4993df773183704bb31634e0bd
> > > Author:     Peter Zijlstra<peterz@xxxxxxxxxxxxx>
> > > AuthorDate: Fri, 10 Jan 2014 21:06:03 +0100
> > > Committer:  Ingo Molnar<mingo@xxxxxxxxxx>
> > > CommitDate: Thu, 16 Jan 2014 09:19:48 +0100
> > >
> > > x86, mm, perf: Allow recursive faults from interrupts
> > >
> > > Waiman managed to trigger a PMI while in a emulate_vsyscall() fault,
> > > the PMI in turn managed to trigger a fault while obtaining a stack
> > > trace. This triggered the sig_on_uaccess_error recursive fault logic
> > > and killed the process dead.
> > >
> > > Fix this by explicitly excluding interrupts from the recursive fault
> > > logic.
> > >
> > > Reported-and-Tested-by: Waiman Long<waiman.long@xxxxxx>
> > > Fixes: e00b12e64be9 ("perf/x86: Further optimize copy_from_user_nmi()")
> > > Cc: Aswin Chandramouleeswaran<aswin@xxxxxx>
> > > Cc: Scott J Norton<scott.norton@xxxxxx>
> > > Cc: Linus Torvalds<torvalds@xxxxxxxxxxxxxxxxxxxx>
> > > Cc: Andy Lutomirski<luto@xxxxxxxxxxxxxx>
> > > Cc: Arnaldo Carvalho de Melo<acme@xxxxxxxxxxxxxxxxxx>
> > > Cc: Andrew Morton<akpm@xxxxxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Peter Zijlstra<peterz@xxxxxxxxxxxxx>
> > > Link:
> > > http://lkml.kernel.org/r/20140110200603.GJ7572@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > > Signed-off-by: Ingo Molnar<mingo@xxxxxxxxxx>
> > > ---
> > >    arch/x86/mm/fault.c | 18 ++++++++++++++++++
> > >    1 file changed, 18 insertions(+)
> > Will that be picked up by Linus as it is a 3.13 regression?
> Does anyone actually know why this regressed recently?  The buggy code
> has been there for quite a while.
>
> --Andy

Yes, the bug was there for a while, but a recent change by Peter (see 
the "Fixes:" line above) made it much easier to hit it.

-Longman
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