kill-the-bkl/reiserfs: move the concurrent tree accesses checks per superblock
When do_balance() balances the tree, a trick is performed to
provide the ability for other tree writers/readers to check whether
do_balance() is executing concurrently (requires CONFIG_REISERFS_CHECK).
This is done to protect concurrent accesses to the tree. The trick
is the following:
When do_balance is called, a unique global variable called cur_tb
takes a pointer to the current tree to be rebalanced.
Once do_balance finishes its work, cur_tb takes the NULL value.
Then, concurrent tree readers/writers just have to check the value
of cur_tb to ensure do_balance isn't executing concurrently.
If it is, then it proves that schedule() occured on do_balance(),
which then relaxed the bkl that protected the tree.
Now that the bkl has be turned into a mutex, this check is still
fine even though do_balance() becomes preemptible: the write lock
will not be automatically released on schedule(), so the tree is
still protected.
But this is only fine if we have a single reiserfs mountpoint.
Indeed, because the bkl is a global lock, it didn't allowed
concurrent executions between a tree reader/writer in a mount point
and a do_balance() on another tree from another mountpoint.
So assuming all these readers/writers weren't supposed to be
reentrant, the current check now sometimes detect false positives with
the current per-superblock mutex which allows this reentrancy.
This patch keeps the concurrent tree accesses check but moves it
per superblock, so that only trees from a same mount point are
checked to be not accessed concurrently.
[ Impact: fix spurious panic while running several reiserfs mount-points ]
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
diff --git a/fs/reiserfs/fix_node.c b/fs/reiserfs/fix_node.c
index 3a685e3..d2f3133 100644
--- a/fs/reiserfs/fix_node.c
+++ b/fs/reiserfs/fix_node.c
@@ -563,9 +563,6 @@
return needed_nodes;
}
-#ifdef CONFIG_REISERFS_CHECK
-extern struct tree_balance *cur_tb;
-#endif
/* Set parameters for balancing.
* Performs write of results of analysis of balancing into structure tb,
@@ -2368,7 +2365,7 @@
return REPEAT_SEARCH;
}
#ifdef CONFIG_REISERFS_CHECK
- if (cur_tb) {
+ if (REISERFS_SB(tb->tb_sb)->cur_tb) {
print_cur_tb("fix_nodes");
reiserfs_panic(tb->tb_sb, "PAP-8305",
"there is pending do_balance");