On Wed, May 29, 2019 at 02:55:57PM +0200, Peter Zijlstra wrote:
> On Wed, May 29, 2019 at 11:20:22AM +0100, Will Deacon wrote:
> > Anyway, you can add my ack to your patch, but I bet we can remove that mm
> > check :D
>
> I've ended up with the below. Ravi, can you test if that does indeed
> obsolete your PPC patch?
>
> ---
> Subject: perf: Fix perf_sample_regs_user()
> From: Peter Zijlstra <pet...@infradead.org>
> Date: Wed May 29 14:37:24 CEST 2019
>
> perf_sample_regs_user() uses 'current->mm' to test for the presence of
> userspace, but this is insufficient, consider use_mm().
>
> A better test is: '!(current->flags & PF_KTHREAD)', exec() clears
> PF_KTHREAD after it sets the new ->mm but before it drops to userspace
> for the first time.
>
> Possibly obsoletes: bf05fc25f268 ("powerpc/perf: Fix oops when kthread execs
> user process")
>
> Reported-by: Ravi Bangoria <ravi.bango...@linux.vnet.ibm.com>
> Reported-by: Young Xiao <92siuy...@gmail.com>
> Cc: Ravi Bangoria <ravi.bango...@linux.vnet.ibm.com>
> Cc: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
> Cc: Michael Ellerman <m...@ellerman.id.au>
> Cc: Jiri Olsa <jo...@redhat.com>
> Cc: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Stephane Eranian <eran...@google.com>
> Cc: Arnaldo Carvalho de Melo <a...@redhat.com>
> Acked-by: Will Deacon <will.dea...@arm.com>
> Fixes: 4018994f3d87 ("perf: Add ability to attach user level registers dump
> to sample")
> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> ---
> kernel/events/core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5923,7 +5923,7 @@ static void perf_sample_regs_user(struct
> if (user_mode(regs)) {
Hmm, so it just occurred to me that Mark's observation is that the regs
can be junk in some cases. In which case, should we be checking for
kthreads first?
Will
