On 08/13, Jan Kara wrote:
>
> Regarding the routing, ideally Al Viro should take these as a VFS
> maintainer.
Al, could you take these patches?
Only cosmetic changes in V3 to address the comments from Jan, I
preserved his acks.
In case you missed all the spam I sent before, let me repeat that
the awful (and currently unneeded) 7/8 will be reverted later. We
need it to ensure that other percpu_rw_semaphore changes routed
via another tree won't break fs/super.c. After that we will add
rcu_sync_dtor(s_writers->rw_sem) into deactivate_locked_super()
and revert this horror.
3/8 documents the lockdep problems we currently have. This is fixed
by the patch below but it depends on xfs ILOCK fixes from Dave, so
I will send it later. Plus another patch which removes the "trylock"
hack in __sb_start_write().
Oleg.
arch/Kconfig | 1 -
fs/btrfs/transaction.c | 8 +--
fs/super.c | 184 +++++++++++++++++++---------------------
fs/xfs/xfs_aops.c | 6 +-
include/linux/fs.h | 23 +++---
include/linux/percpu-rwsem.h | 20 +++++
init/Kconfig | 1 -
kernel/locking/Makefile | 3 +-
kernel/locking/percpu-rwsem.c | 13 +++
lib/Kconfig | 3 -
10 files changed, 136 insertions(+), 126 deletions(-)
--------------------------------------------------------------------------
[PATCH v3 9/8] don't fool lockdep in freeze_super() and thaw_super() paths
sb_wait_write()->percpu_rwsem_release() fools lockdep to avoid the
false-positives. Now that xfs was fixed by Dave we can remove it and
change freeze_super() and thaw_super() to run with s_writers.rw_sem
locks held; we add two trivial helpers for that, sb_freeze_release()
and sb_freeze_acquire().
Signed-off-by: Oleg Nesterov <o...@redhat.com>
Reviewed-by: Jan Kara <j...@suse.com>
---
fs/super.c | 37 +++++++++++++++++++++++++------------
1 files changed, 25 insertions(+), 12 deletions(-)
diff --git a/fs/super.c b/fs/super.c
index 4350ff4..91c9756 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1213,25 +1213,34 @@ EXPORT_SYMBOL(__sb_start_write);
static void sb_wait_write(struct super_block *sb, int level)
{
percpu_down_write(sb->s_writers.rw_sem + level-1);
- /*
- * We are going to return to userspace and forget about this lock, the
- * ownership goes to the caller of thaw_super() which does unlock.
- *
- * FIXME: we should do this before return from freeze_super() after we
- * called sync_filesystem(sb) and s_op->freeze_fs(sb), and thaw_super()
- * should re-acquire these locks before s_op->unfreeze_fs(sb). However
- * this leads to lockdep false-positives, so currently we do the early
- * release right after acquire.
- */
- percpu_rwsem_release(sb->s_writers.rw_sem + level-1, 0, _THIS_IP_);
}
-static void sb_freeze_unlock(struct super_block *sb)
+/*
+ * We are going to return to userspace and forget about these locks, the
+ * ownership goes to the caller of thaw_super() which does unlock().
+ */
+static void sb_freeze_release(struct super_block *sb)
+{
+ int level;
+
+ for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
+ percpu_rwsem_release(sb->s_writers.rw_sem + level, 0,
_THIS_IP_);
+}
+
+/*
+ * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).
+ */
+static void sb_freeze_acquire(struct super_block *sb)
{
int level;
for (level = 0; level < SB_FREEZE_LEVELS; ++level)
percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0,
_THIS_IP_);
+}
+
+static void sb_freeze_unlock(struct super_block *sb)
+{
+ int level;
for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
percpu_up_write(sb->s_writers.rw_sem + level);
@@ -1327,6 +1336,7 @@ int freeze_super(struct super_block *sb)
* sees write activity when frozen is set to SB_FREEZE_COMPLETE.
*/
sb->s_writers.frozen = SB_FREEZE_COMPLETE;
+ sb_freeze_release(sb);
up_write(&sb->s_umount);
return 0;
}
@@ -1353,11 +1363,14 @@ int thaw_super(struct super_block *sb)
goto out;
}
+ sb_freeze_acquire(sb);
+
if (sb->s_op->unfreeze_fs) {
error = sb->s_op->unfreeze_fs(sb);
if (error) {
printk(KERN_ERR
"VFS:Filesystem thaw failed\n");
+ sb_freeze_release(sb);
up_write(&sb->s_umount);
return error;
}
--
1.5.5.1
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