diff options
author | Jeff Layton <jlayton@redhat.com> | 2013-06-21 08:58:15 -0400 |
---|---|---|
committer | Al Viro <viro@zeniv.linux.org.uk> | 2013-06-29 12:57:42 +0400 |
commit | 1c8c601a8c0dc59fe64907dcd9d512a3d181ddc7 (patch) | |
tree | 1a9c91de460a7c2f9fd6ad77060be484456e49b9 /Documentation/filesystems | |
parent | 889746917193ab3007a779d65231510715b20fb6 (diff) |
locks: protect most of the file_lock handling with i_lock
Having a global lock that protects all of this code is a clear
scalability problem. Instead of doing that, move most of the code to be
protected by the i_lock instead. The exceptions are the global lists
that the ->fl_link sits on, and the ->fl_block list.
->fl_link is what connects these structures to the
global lists, so we must ensure that we hold those locks when iterating
over or updating these lists.
Furthermore, sound deadlock detection requires that we hold the
blocked_list state steady while checking for loops. We also must ensure
that the search and update to the list are atomic.
For the checking and insertion side of the blocked_list, push the
acquisition of the global lock into __posix_lock_file and ensure that
checking and update of the blocked_list is done without dropping the
lock in between.
On the removal side, when waking up blocked lock waiters, take the
global lock before walking the blocked list and dequeue the waiters from
the global list prior to removal from the fl_block list.
With this, deadlock detection should be race free while we minimize
excessive file_lock_lock thrashing.
Finally, in order to avoid a lock inversion problem when handling
/proc/locks output we must ensure that manipulations of the fl_block
list are also protected by the file_lock_lock.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'Documentation/filesystems')
-rw-r--r-- | Documentation/filesystems/Locking | 21 |
1 files changed, 14 insertions, 7 deletions
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking index f94a362f408e..c2963a74fbc3 100644 --- a/Documentation/filesystems/Locking +++ b/Documentation/filesystems/Locking @@ -342,7 +342,7 @@ prototypes: locking rules: - file_lock_lock may block + inode->i_lock may block fl_copy_lock: yes no fl_release_private: maybe no @@ -355,12 +355,19 @@ prototypes: int (*lm_change)(struct file_lock **, int); locking rules: - file_lock_lock may block -lm_compare_owner: yes no -lm_notify: yes no -lm_grant: no no -lm_break: yes no -lm_change yes no + + inode->i_lock file_lock_lock may block +lm_compare_owner: yes[1] maybe no +lm_notify: yes yes no +lm_grant: no no no +lm_break: yes no no +lm_change yes no no + +[1]: ->lm_compare_owner is generally called with *an* inode->i_lock held. It +may not be the i_lock of the inode for either file_lock being compared! This is +the case with deadlock detection, since the code has to chase down the owners +of locks that may be entirely unrelated to the one on which the lock is being +acquired. When doing a search for deadlocks, the file_lock_lock is also held. --------------------------- buffer_head ----------------------------------- prototypes: |