On Mon, Jul 23, 2012 at 02:20:57PM +0200, Lukáš Czerner wrote: [cut...] > > > Moreover I think that we should avoid taking i_mutex if we can and I > > > believe that we can in this case, because we only need to prevent > > > allocation. So I just want to let you know that this part is > > > probably going to change anyway. > > > > It seems that we need to take i_mutex locking to prevent from buffered > > writes after page cache has been truncated by truncate_pagecache_range. > > If a buffered write without delalloc occurs after truncating page cache > > and before taking i_data_sem, that means that the allocated block for > > this buffered write will be removed in ext4_ext_remove_space when the > > offset is within the range of the hole. Am I missing something? > > You're absolutely right, currently this is possible. But I think that we > can take i_data_sem before truncating the pagecache hence preventing anyone > from mapping new blocks. However this is not yet implemented in my > patch set. > > ... > hmm, looking at the ext4_write_begin() it seems like it might not be > such good idea after all. It seems to take page lock before > i_data_sem so we might get deadlock, moreover if the punch hole > happened in the middle of the ext4_write_begin() we might have only > part of the data written, moreover this does not have to be hole > aligned, which is bad. I need to revise that. Yes, this is why I think that i_mutex locking should be taken. At least we are safty when we take the i_mutex. :-) Regards, Zheng -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
