On 07/21, Jan Kara wrote: > > On Mon 20-07-15 19:01:03, 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(). > > The patch looks good. Did you test this BTW? You can add: Yes, but "artificially". I just wrote the function which takes/drops SB_FREEZE_FS twice with and then without SB_FREEZE_WRITE. It worked as expected, lockdep complained when SB_FREEZE_WRITE wasn't held. > Reviewed-by: Jan Kara <jack@xxxxxxxx> Thanks! Oleg. -- 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
