On Tue 11-08-15 19:04:01, Oleg Nesterov wrote: > 1. wait_event(frozen < level) without rwsem_acquire_read() is just > wrong from lockdep perspective. If we are going to deadlock > because the caller is buggy, lockdep detect this problem. > > 2. __sb_start_write() can race with thaw_super() + freeze_super(), > and after "goto retry" the 2nd acquire_freeze_lock() is wrong. > > 3. The "tell lockdep we are doing trylock" hack doesn't look nice. > > I think this is correct, but this logic should be more explicit. > Yes, the recursive read_lock() is fine if we hold the lock on a > higher level. But we do not need to fool lockdep. If we can not > deadlock in this case then try-lock must not fail and we can use > use wait == F throughout this code. > > Note: as Dave Chinner explains, the "trylock" hack and the fat comment > can be probably removed. But this needs a separate change and it will > be trivial: just kill __sb_start_write() and rename do_sb_start_write() > back to __sb_start_write(). > > Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Just a nit below... > + if (wait) > + rwsem_acquire_read(&sb->s_writers.lock_map[level-1], 0, 0, ip); If we provided also __sb_writers_acquire() helper (in addition to _nowait) variant, we could use these helpers in __sb_start_write() / __sb_end_write() as well which would look better to me when we already have them. Once this is updated, feel free to add: Reviewed-by: Jan Kara <jack@xxxxxxxx> Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
