On Thu, 22 Mar 2012 03:41:09 +0000, Al Viro wrote: > On Thu, Mar 22, 2012 at 11:13:15AM +0800, Miao Xie wrote: >> Some file systems can do some works in the background by kthreads, we'd >> better stop those works before we umount the file system, or it is easy to >> introduce some problems. So we add an interface that is used to do some >> preparation for umount. > > NAK. First of all, fs might be in active use _after_ umount. man 8 umount, > see umount -l there. Moreover, the same superblock may very well be mounted > more than once, so umount of an individual mountpoint would better not do > anything nasty to users of other ones. > > IOW, this is completely misguided - you are dealing with whatever problem it > is at least two layers above the right one. > > 1) vfsmount may be detached from mount trees but remain in active use. > 2) there may be many vfsmounts over given struct super_block. > > Doing things earlier than the final mntput() runs afoul of (1); doing > them before the final deactivate_locked_super() runs afoul of (2). > > What the hell is that thread doing that needs ->s_umount for serialization > and why is it doing that?
AFAIK, acquiring ->s_umount is to avoid the filesystem going from r/w to r/o. This is patch is slapdash, I will find another way to deal with the bug we found. Thanks for your review. Miao -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
