On Tue, 12 Aug 2014 10:48:08 -0400 Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote: > In the days of yore, the file locking code was primarily protected by > the BKL. That changed in commit 72f98e72551fa (locks: turn lock_flocks > into a spinlock), at which point the code was changed to be protected > by a conventional spinlock (mostly due to a push to finally eliminate > the BKL). Since then, the code has been changed to use the i_lock > instead of a global spinlock, but it's still under a spinlock. > > With that change, several functions now no longer can block when they > originally could. This is a particular problem with the > fl_release_private operation. In NFSv4, that operation is used to kick > off a RELEASE_LOCKOWNER or FREE_STATEID call, and that requires being > able to do an allocation. > > This was reported by Josh Stone here: > > https://bugzilla.redhat.com/show_bug.cgi?id=1089092 > > My initial stab at fixing this involved moving this to a workqueue, but > Trond pointed out the above change was technically a regression with the > way the spinlocking in the file locking code works, and suggested an > alternate approach to fixing it. > > This set focuses on moving most of the locks_release_private calls > outside of the inode->i_lock. There are still a few that are done > under the i_lock in the lease handling code. Cleaning up the use of > the i_lock in the lease code is a larger project which we'll have to > tackle at some point, but there are some other cleanups that will > need to happen first. > > Absent any objections, I'll plan to merge these for 3.18. > Erm...make that v3.17... As Trond points out, the fact that we end up doing sleeping allocations under spinlock can allow an unprivileged user to crash a NFSv4 client. So I may see about merging these sooner rather than later after they've had a little soak time in linux-next. -- Jeff Layton <jlayton@xxxxxxxxxxxxxxx> -- 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
