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| author |   Al Viro <viro@zeniv.linux.org.uk> | 2013-09-29 22:06:07 -0400 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2013-11-09 00:16:19 -0500 |
| commit | 48a066e72d970a3e225a9c18690d570c736fc455 (patch) | |
| tree | 9a1861c1be4309cf69964742d238eadd5d0b1832 /include/linux/mount.h | |
| parent | switch shrink_dcache_for_umount() to use of d_walk() (diff) | |
| download | linux-dev-48a066e72d970a3e225a9c18690d570c736fc455.tar.xz linux-dev-48a066e72d970a3e225a9c18690d570c736fc455.zip | |
RCU'd vfsmounts
* RCU-delayed freeing of vfsmounts
* vfsmount_lock replaced with a seqlock (mount_lock)
* sequence number from mount_lock is stored in nameidata->m_seq and
used when we exit RCU mode
* new vfsmount flag - MNT_SYNC_UMOUNT. Set by umount_tree() when its
caller knows that vfsmount will have no surviving references.
* synchronize_rcu() done between unlocking namespace_sem in namespace_unlock()
and doing pending mntput().
* new helper: legitimize_mnt(mnt, seq). Checks the mount_lock sequence
number against seq, then grabs reference to mnt. Then it rechecks mount_lock
again to close the race and either returns success or drops the reference it
has acquired. The subtle point is that in case of MNT_SYNC_UMOUNT we can
simply decrement the refcount and sod off - aforementioned synchronize_rcu()
makes sure that final mntput() won't come until we leave RCU mode. We need
that, since we don't want to end up with some lazy pathwalk racing with
umount() and stealing the final mntput() from it - caller of umount() may
expect it to return only once the fs is shut down and we don't want to break
that. In other cases (i.e. with MNT_SYNC_UMOUNT absent) we have to do
full-blown mntput() in case of mount_lock sequence number mismatch happening
just as we'd grabbed the reference, but in those cases we won't be stealing
the final mntput() from anything that would care.
* mntput_no_expire() doesn't lock anything on the fast path now. Incidentally,
SMP and UP cases are handled the same way - no ifdefs there.
* normal pathname resolution does *not* do any writes to mount_lock. It does,
of course, bump the refcounts of vfsmount and dentry in the very end, but that's
it.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'include/linux/mount.h')
| -rw-r--r-- | include/linux/mount.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/include/linux/mount.h b/include/linux/mount.h index 38cd98f112a0..371d346fa270 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -49,6 +49,8 @@ struct mnt_namespace; #define MNT_LOCK_READONLY 0x400000 #define MNT_LOCKED 0x800000 +#define MNT_DOOMED 0x1000000 +#define MNT_SYNC_UMOUNT 0x2000000 struct vfsmount { struct dentry *mnt_root; /* root of the mounted tree */ |