On Mon 15-07-24 10:22:03, Josef Bacik wrote: > On Mon, Jul 15, 2024 at 03:04:10PM +0200, Jan Kara wrote: > > When __fsnotify_recalc_mask() recomputes the mask on the watched object, > > the compiler can "optimize" the code to perform partial updates to the > > mask (including zeroing it at the beginning). Thus places checking > > the object mask without conn->lock such as fsnotify_object_watched() > > could see invalid states of the mask. Make sure the mask update is > > performed by one memory store using WRITE_ONCE(). > > > > Reported-by: syzbot+701037856c25b143f1ad@xxxxxxxxxxxxxxxxxxxxxxxxx > > Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > > Link: https://lore.kernel.org/all/CACT4Y+Zk0ohwwwHSD63U2-PQ=UuamXczr1mKBD6xtj2dyYKBvA@xxxxxxxxxxxxxx > > Signed-off-by: Jan Kara <jack@xxxxxxx> > > I'm still hazy on the rules here and what KCSAN expects, but if we're using > READ_ONCE/WRITE_ONCE on a thing, do we have to use them everywhere we access > that member? Because there's a few accesses in include/linux/fsnotify_backend.h > that were missed if so. Thanks, Indeed there are two accesses there that should be using READ_ONCE() as well. I've missed those. Thanks for review! Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
