git: DragonFly_RELEASE_4_6 kernel - Close a few SMP holes
dillon at crater.dragonflybsd.org
Mon Jul 25 14:35:34 PDT 2016
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date: Sun Jul 24 21:55:00 2016 -0700
kernel - Close a few SMP holes
* Don't trust the compiler when loading refs in cache_zap(). Make sure
it doesn't reorder or re-use the memory reference.
* In cache_nlookup() and cache_nlookup_maybe_shared(), do a full re-test
of the namecache element after locking instead of a partial re-test.
* Lock the namecache record in two situations where we need to set a
flag. Almost all other flag cases require similar locking. This fixes
a potential SMP race in a very thin window during mounting.
* Fix unmount / access races in sys_vquotactl() and, more importantly, in
sys_mount(). We were disposing of the namecache record after extracting
the mount pointer, then using the mount pointer. This could race an
unmount and result in a corrupt mount pointer.
Change the code to dispose of the namecache record after we finish using
the mount point. This is somewhat more complex then I'd like, but it
is important to unlock the namecache record across the potentially
blocking operation to prevent a lock chain from propagating upwards
towards the root.
* Enhanced debugging for the namecache teardown case when nc_refs changes
* Remove some dead code (cache_purgevfs()).
Summary of changes:
sys/kern/vfs_cache.c | 62 ++++++++++++++-----------------------------------
sys/kern/vfs_conf.c | 9 ++++++-
sys/kern/vfs_quota.c | 31 ++++++++++++++-----------
sys/kern/vfs_syscalls.c | 37 ++++++++++++++++++++++-------
4 files changed, 72 insertions(+), 67 deletions(-)
DragonFly BSD source repository
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