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 <[email protected]> > 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 <[email protected]> > Reported-by: Young Xiao <[email protected]> > Cc: Ravi Bangoria <[email protected]> > Cc: Naveen N. Rao <[email protected]> > Cc: Michael Ellerman <[email protected]> > Cc: Jiri Olsa <[email protected]> > Cc: Frederic Weisbecker <[email protected]> > Cc: Stephane Eranian <[email protected]> > Cc: Arnaldo Carvalho de Melo <[email protected]> > Acked-by: Will Deacon <[email protected]> > Fixes: 4018994f3d87 ("perf: Add ability to attach user level registers dump > to sample") > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > --- > 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
