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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 /fs/file.c | |
| 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 'fs/file.c')
| -rw-r--r-- | fs/file.c | 4 |
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); |