On Mon, Oct 07, 2019 at 12:40:39PM +0200, Andrea Parri wrote: > Hi Christian, > > On Mon, Oct 07, 2019 at 01:52:16AM +0200, Christian Brauner wrote: > > When assiging and testing taskstats in taskstats_exit() there's a race > > when writing and reading sig->stats when a thread-group with more than > > one thread exits: > > > > cpu0: > > thread catches fatal signal and whole thread-group gets taken down > > do_exit() > > do_group_exit() > > taskstats_exit() > > taskstats_tgid_alloc() > > The tasks reads sig->stats holding sighand lock seeing garbage. > > > > cpu1: > > task calls exit_group() > > do_exit() > > do_group_exit() > > taskstats_exit() > > taskstats_tgid_alloc() > > The task takes sighand lock and assigns new stats to sig->stats. > > > > Fix this by using READ_ONCE() and smp_store_release(). > > > > Reported-by: syzbot+c5d03165a1bd1dead...@syzkaller.appspotmail.com > > Cc: Dmitry Vyukov <dvyu...@google.com> > > Signed-off-by: Christian Brauner <christian.brau...@ubuntu.com> > > FYI, checkpatch.pl says: > > WARNING: memory barrier without comment > #62: FILE: kernel/taskstats.c:568: > + smp_store_release(&sig->stats, stats_new); > > Maybe you can make checkpatch.pl happy ;-) and add a comment to stress > the 'pairing' between this barrier and the added READ_ONCE() (as Dmitry > was alluding to in a previous post)?
Of course. I totally forgot the memory barrier documentation requirement. Christian
