Am 28.02.2014 14:29, schrieb Alexander Viro:
On Fri, Feb 28, 2014 at 01:12:58PM +0100, Donald Buczek wrote:Obviously, "cleared mounted on dentry" is missing. It looks like we enter put_mountpoint() but don't get to dentry->d_flags &= ~DCACHE_MOUNTED; mp->m_count is not zero probably. What does it mean? The mount is still locked but not in the mount hash?No, it means that something else is mounted on the same dentry (in another part of mount tree, obviously). If you mount the same fs on two different mountpoints, e.g. mount /dev/sda1 /mnt mount /dev/sda1 /tmp/foo you will have the same dentries seen in two places. Now, mount /dev/sdb11 /mnt/a mount /dev/sdc5 /tmp/foo/a and you've got two different filesystems mounted on two different places (/mnt/a and /tmp/foo/a). These two places have different vfsmounts, but the same dentry. struct mountpoint is associated with dentry, so it's also the same for both. And it serves as a mountpoint for two vfsmounts - one for fs from sdb11, another for fs from sdc5. Now umount /mnt/a; one of those two vfsmounts is gone now. struct mountpoint survives, of course, and dentry is *still* a mountpoint. sdc5 is still mounted on /tmp/foo/a, after all...
Thanks. So I guess, the idea of "struct mountpoint" is to make the dentries smaller by not having the mount count embedded in each one, 99.9% not needing it?
OMG, I've just found this in the log:
91286 2014-02-26T14:09:56.830515+01:00 kasslerbraten kernel: [195977.007799] pid 8644: d_set_mounted: dentry=ffff88004690c710 root 91287 2014-02-26T14:09:56.830527+01:00 kasslerbraten kernel: [195977.007802] pid 8644: d_set_mounted: set mounted on dentry=ffff88004690c710 root 91288 2014-02-26T14:09:56.830529+01:00 kasslerbraten kernel: [195977.007873] pid 8644: put_mountpoint: mp=ffff8800b8aa1a38 91289 2014-02-26T14:09:56.830530+01:00 kasslerbraten kernel: [195977.007877] pid 8644: d_set_mounted: dentry=ffff8800ca45e810 tmp 91290 2014-02-26T14:09:56.830535+01:00 kasslerbraten kernel: [195977.007878] pid 8644: d_set_mounted: set mounted on dentry=ffff8800ca45e810 tmp 91291 2014-02-26T14:09:56.830536+01:00 kasslerbraten kernel: [195977.007881] pid 8644: put_mountpoint: mp=ffff8800b8aa1a38 91292 2014-02-26T14:09:56.830537+01:00 kasslerbraten kernel: [195977.007900] pid 8644: d_set_mounted: dentry=ffff880046960450 old-root-mjn70Q 91293 2014-02-26T14:09:56.830538+01:00 kasslerbraten kernel: [195977.007901] pid 8644: d_set_mounted: set mounted on dentry=ffff880046960450 old-root-mjn70Q 91294 2014-02-26T14:09:56.830539+01:00 kasslerbraten kernel: [195977.007903] pid 8644: put_mountpoint: mp=ffff8800a5f1dbd0 91295 2014-02-26T14:09:56.830540+01:00 kasslerbraten kernel: [195977.007904] pid 8644: put_mountpoint: cleared mounted on dentry=ffff88004690c710 root 91296 2014-02-26T14:09:56.830541+01:00 kasslerbraten kernel: [195977.007905] pid 8644: put_mountpoint: mp=ffff8800a5f1da90 91297 2014-02-26T14:09:56.830541+01:00 kasslerbraten kernel: [195977.007954] pid 8644: put_mountpoint: mp=0000014f00490049 91298 2014-02-26T14:09:56.830542+01:00 kasslerbraten kernel: [195977.007955] pid 8644: put_mountpoint: mp=0000000000000006 91299 2014-02-26T14:09:56.830543+01:00 kasslerbraten kernel: [195977.007961] pid 8644: put_mountpoint: mp=ffff8800a5f1dbd0 91300 2014-02-26T14:09:56.830544+01:00 kasslerbraten kernel: [195977.007963] pid 8644: put_mountpoint: mp=ffff8800a6023d10 91301 2014-02-26T14:09:56.830544+01:00 kasslerbraten kernel: [195977.007963] pid 8644: put_mountpoint: mp=ffff8800a6023d10 91302 2014-02-26T14:09:56.830545+01:00 kasslerbraten kernel: [195977.007964] pid 8644: put_mountpoint: mp=ffff8800a5f1dbd0
What is this? Where does "root" and "old-root-" come from? Why does 8644 survive dereferencing mp=0000000000000006 from the kernel? Is this still related to autofs?
D. -- Donald Buczek buczek@xxxxxxxxxxxxx Tel: +49 30 8413 1433
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