On Fri, 30 Jan 2015 02:14:45 +0000, Al Viro wrote: > On Fri, Jan 30, 2015 at 09:44:03AM +0800, Qu Wenruo wrote: > >> This shouldn't happen. If someone is ro, the whole fs should be ro, right? > > Wrong. Individual vfsmounts over an r/w superblock might very well be r/o. > As for that trylock... What for? It invites transient failures for no > good reason. Removal of sysfs entry will block while write(2) to that sucker > is in progress, so btrfs shutdown will block at that point in ctree_close(). > It won't go away under you. could you explain the race condition? I think the deadlock won't happen, during the btrfs shutdown, we hold s_umount, the write operation will fail to lock it, and quit quickly, and then umount will continue. I think sb_want_write() is similar to trylock(s_umount), the difference is that sb_want_write() is more complex. > > Now, you might want to move those sysfs entry removals to the very beginning > of btrfs_kill_super(), but that's a different story - you need only to make > sure that they are removed not later than the destruction of the data > structures they need (IOW, the current location might very well be OK - I > hadn't checked the details). Yes, we need move those sysfs entry removals, but needn't move to the very beginning of btrfs_kill_super(), just at the beginning of close_ctree(); The current location is not right, it will introduce the use-after-free problem. because we remove the sysfs entry after we release transaction_kthread, use-after-free problem might happen in this case Task1 Task2 change Label by sysfs close_ctree kthread_stop(transaction_kthread); change label wake_up(transaction_kthread) Thanks Miao > > As for "it won't go r/o under us" - sb_want_write() will do that just fine. > . > -- 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
