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| author | Oleg Nesterov <oleg@redhat.com> | 2014-01-11 22:19:32 +0400 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2014-01-25 12:14:36 +0400 |
| commit | a8d4b8345e0ee48b732126d980efaf0dc373e2b0 (patch) | |
| tree | 4bdfc52ef4ad176f54e4ce7b81091c0fbef0fd04 /include/linux/rcupdate.h | |
| parent | 2ccdc413196b43a02bb68b46be5b68850904e9ea (diff) | |
| download | linux-a8d4b8345e0ee48b732126d980efaf0dc373e2b0.tar.xz | |
introduce __fcheck_files() to fix rcu_dereference_check_fdtable(), kill rcu_my_thread_group_empty()
rcu_dereference_check_fdtable() looks very wrong,
1. rcu_my_thread_group_empty() was added by 844b9a8707f1 "vfs: fix
RCU-lockdep false positive due to /proc" but it doesn't really
fix the problem. A CLONE_THREAD (without CLONE_FILES) task can
hit the same race with get_files_struct().
And otoh rcu_my_thread_group_empty() can suppress the correct
warning if the caller is the CLONE_FILES (without CLONE_THREAD)
task.
2. files->count == 1 check is not really right too. Even if this
files_struct is not shared it is not safe to access it lockless
unless the caller is the owner.
Otoh, this check is sub-optimal. files->count == 0 always means
it is safe to use it lockless even if files != current->files,
but put_files_struct() has to take rcu_read_lock(). See the next
patch.
This patch removes the buggy checks and turns fcheck_files() into
__fcheck_files() which uses rcu_dereference_raw(), the "unshared"
callers, fget_light() and fget_raw_light(), can use it to avoid
the warning from RCU-lockdep.
fcheck_files() is trivially reimplemented as rcu_lockdep_assert()
plus __fcheck_files().
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'include/linux/rcupdate.h')
| -rw-r--r-- | include/linux/rcupdate.h | 2 |
1 files changed, 0 insertions, 2 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 39cbb889e20d..a2482cf90b6b 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -448,8 +448,6 @@ static inline int rcu_read_lock_sched_held(void) #ifdef CONFIG_PROVE_RCU -extern int rcu_my_thread_group_empty(void); - /** * rcu_lockdep_assert - emit lockdep splat if specified condition not met * @c: condition to check |