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Differential D59982

lockf: Do not block in vfs_busy()
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Authored by markj on Thu, Sep 24, 1:51 PM.
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kib
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rGf117b6ba9f7c: lockf: Do not block in vfs_busy()
rGa5d112ba16b3: lockf: Do not block in vfs_busy()
rGdd16a5f53b0b: lockf: Do not block in vfs_busy()
Summary

I believe a race is possible otherwise: vfs_busy() may return after an
unmounted filesystem has been removed from the global mount list.
That is, vfs_busy() will block until vfs_mount_destroy() sets
MNTK_REFEXPIRE, and at that point the mountpoint has been removed from
the mountlist, so TAILQ_FOREACH can return an invalid value.

Simply do not block if the mountpoint is being unmounted.

Fixes: eca39864f702 ("Add sysctl KERN_LOCKF")

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rG FreeBSD src repository
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sys/
kern/
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sys/kern/kern_lockf.c

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