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Date: Tue, 10 Jun 2008 08:28:48 +0200 From: Jesper Krogh <jesper@...gh.cc> To: Ian Kent <raven@...maw.net> CC: Al Viro <viro@...IV.linux.org.uk>, Jeff Moyer <jmoyer@...hat.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Miklos Szeredi <miklos@...redi.hu>, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org Subject: Re: Linux 2.6.26-rc4 Ian Kent wrote: > On Wed, 2008-06-04 at 10:42 +0800, Ian Kent wrote: >> On Wed, 2008-06-04 at 00:00 +0100, Al Viro wrote: >>> On Tue, Jun 03, 2008 at 03:53:36PM -0400, Jeff Moyer wrote: >>> >>>> autofs4_lookup is called on behalf a process trying to walk into an >>>> automounted directory. That dentry's d_flags is set to >>>> DCACHE_AUTOFS_PENDING but not hashed. A waitqueue entry is created, >>>> indexed off of the name of the dentry. A callout is made to the >>>> automount daemon (via autofs4_wait). >>>> >>>> The daemon looks up the directory name in its configuration. If it >>>> finds a valid map entry, it will then create the directory using >>>> sys_mkdir. The autofs4_lookup call on behalf of the daemon (oz_mode == >>>> 1) will return NULL, and then the mkdir call will be made. The >>>> autofs4_mkdir function then instantiates the dentry which, by the way, >>>> is different from the original dentry passed to autofs4_lookup. (This >>>> dentry also does not get the PENDING flag set, which is a bug addressed >>>> by a patch set that Ian and I have been working on; specifically, the >>>> idea is to reuse the dentry from the original lookup, but I digress). >>>> >>>> The daemon then mounts the share on the given directory and issues an >>>> ioctl to wakeup the waiter. When awakened, the waiter clears the >>>> DCACHE_AUTOFS_PENDING flag, does another lookup of the name in the >>>> dcache and returns that dentry if found. >>>> Later, the dentry gets expired via another ioctl. That path sets >>>> the AUTOFS_INF_EXPIRING flag in the d_fsdata associated with the dentry. >>>> It then calls out to the daemon to perform the unmount and rmdir. The >>>> rmdir unhashes the dentry (and places it on the rehash list). >>>> >>>> The dentry is removed from the rehash list if there was a racing expire >>>> and mount or if the dentry is released. >>>> >>>> This description is valid for the tree as it stands today. Ian and I >>>> have been working on fixing some other race conditions which will change >>>> the dentry life cycle (for the better, I hope). >>> So what happens if new lookup hits between umount and rmdir? >> It will wait for the expire to complete and then wait for a mount >> request to the daemon. > > Actually, that explanation is a bit simple minded. > > It should wait for the expire in ->revalidate(). > Following the expire completion d_invalidate() should return 0, since > the dentry is now unhashed, which causes ->revalidate() to return 0. > do_lookup() should see this and call a ->lookup(). > > But maybe I've missed something as I'm seeing a problem now. Ok. Ive been running on the patch for a few days now .. and didn't see any problems. But that being said, I also turned off the --ghost option to autofs so if it actually is the patch or the different codepaths being used, I dont know. Since this is a production system, I'm a bit reluctant to just change a working setup to test it out. Jesper -- Jesper -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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