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authorFrederic Weisbecker <fweisbec@gmail.com>2009-05-16 19:10:38 +0200
committerFrederic Weisbecker <fweisbec@gmail.com>2009-09-14 07:18:25 +0200
commit08f14fc8963e585e65b71212ce8050607b9b6c36 (patch)
tree04d808f71193df2a90d485fcc0e2604bd8fe8d93 /fs/reiserfs/do_balan.c
parentc72e05756b900b3be24cd73a16de52bab80984c0 (diff)
downloadlinux-08f14fc8963e585e65b71212ce8050607b9b6c36.tar.bz2
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>
Diffstat (limited to 'fs/reiserfs/do_balan.c')
-rw-r--r--fs/reiserfs/do_balan.c17
1 files changed, 5 insertions, 12 deletions
diff --git a/fs/reiserfs/do_balan.c b/fs/reiserfs/do_balan.c
index 128d3f7c8aa5..60c080440661 100644
--- a/fs/reiserfs/do_balan.c
+++ b/fs/reiserfs/do_balan.c
@@ -21,14 +21,6 @@
#include <linux/buffer_head.h>
#include <linux/kernel.h>
-#ifdef CONFIG_REISERFS_CHECK
-
-struct tree_balance *cur_tb = NULL; /* detects whether more than one
- copy of tb exists as a means
- of checking whether schedule
- is interrupting do_balance */
-#endif
-
static inline void buffer_info_init_left(struct tree_balance *tb,
struct buffer_info *bi)
{
@@ -1840,11 +1832,12 @@ static int check_before_balancing(struct tree_balance *tb)
{
int retval = 0;
- if (cur_tb) {
+ if (REISERFS_SB(tb->tb_sb)->cur_tb) {
reiserfs_panic(tb->tb_sb, "vs-12335", "suspect that schedule "
"occurred based on cur_tb not being null at "
"this point in code. do_balance cannot properly "
- "handle schedule occurring while it runs.");
+ "handle concurrent tree accesses on a same "
+ "mount point.");
}
/* double check that buffers that we will modify are unlocked. (fix_nodes should already have
@@ -1986,7 +1979,7 @@ static inline void do_balance_starts(struct tree_balance *tb)
"check");*/
RFALSE(check_before_balancing(tb), "PAP-12340: locked buffers in TB");
#ifdef CONFIG_REISERFS_CHECK
- cur_tb = tb;
+ REISERFS_SB(tb->tb_sb)->cur_tb = tb;
#endif
}
@@ -1996,7 +1989,7 @@ static inline void do_balance_completed(struct tree_balance *tb)
#ifdef CONFIG_REISERFS_CHECK
check_leaf_level(tb);
check_internal_levels(tb);
- cur_tb = NULL;
+ REISERFS_SB(tb->tb_sb)->cur_tb = NULL;
#endif
/* reiserfs_free_block is no longer schedule safe. So, we need to