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authorOleg Nesterov <oleg@redhat.com>2014-01-11 19:19:32 +0100
committerAl Viro <viro@zeniv.linux.org.uk>2014-01-25 03:14:36 -0500
commita8d4b8345e0ee48b732126d980efaf0dc373e2b0 (patch)
tree4bdfc52ef4ad176f54e4ce7b81091c0fbef0fd04 /fs/file.c
parent2ccdc413196b43a02bb68b46be5b68850904e9ea (diff)
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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 'fs/file.c')
-rw-r--r--fs/file.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/file.c b/fs/file.c
index 4a78f981557a..957cbc09b0db 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -707,7 +707,7 @@ struct file *fget_light(unsigned int fd, int *fput_needed)
*fput_needed = 0;
if (atomic_read(&files->count) == 1) {
- file = fcheck_files(files, fd);
+ file = __fcheck_files(files, fd);
if (file && (file->f_mode & FMODE_PATH))
file = NULL;
} else {
@@ -735,7 +735,7 @@ struct file *fget_raw_light(unsigned int fd, int *fput_needed)
*fput_needed = 0;
if (atomic_read(&files->count) == 1) {
- file = fcheck_files(files, fd);
+ file = __fcheck_files(files, fd);
} else {
rcu_read_lock();
file = fcheck_files(files, fd);