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Date: Sat, 16 May 2009 20:02:02 +0200
From: Frederic Weisbecker <fweisbec@...il.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Reiserfs <reiserfs-devel@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Stephen Rothwell <sfr@...b.auug.org.au>,
Jeff Mahoney <jeffm@...e.com>,
Chris Mason <chris.mason@...cle.com>,
Ingo Molnar <mingo@...e.hu>,
Alexander Beregalov <a.beregalov@...il.com>
Subject: [PATCH 2/2] 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@...e.com>
Cc: Chris Mason <chris.mason@...cle.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Alexander Beregalov <a.beregalov@...il.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
fs/reiserfs/do_balan.c | 17 +++++------------
fs/reiserfs/fix_node.c | 5 +----
fs/reiserfs/prints.c | 4 ----
fs/reiserfs/stree.c | 5 +----
include/linux/reiserfs_fs_sb.h | 11 +++++++++++
5 files changed, 18 insertions(+), 24 deletions(-)
diff --git a/fs/reiserfs/do_balan.c b/fs/reiserfs/do_balan.c
index 4beb964..2787349 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)
{
@@ -1841,11 +1833,12 @@ 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
@@ -1987,7 +1980,7 @@ 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
}
@@ -1997,7 +1990,7 @@ 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
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 @@ static int get_num_ver(int mode, struct tree_balance *tb, int h,
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 @@ int fix_nodes(int op_mode, struct tree_balance *tb,
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");
diff --git a/fs/reiserfs/prints.c b/fs/reiserfs/prints.c
index 536eaca..adbc6f5 100644
--- a/fs/reiserfs/prints.c
+++ b/fs/reiserfs/prints.c
@@ -349,10 +349,6 @@ void reiserfs_debug(struct super_block *s, int level, const char *fmt, ...)
. */
-#ifdef CONFIG_REISERFS_CHECK
-extern struct tree_balance *cur_tb;
-#endif
-
void __reiserfs_panic(struct super_block *sb, const char *id,
const char *function, const char *fmt, ...)
{
diff --git a/fs/reiserfs/stree.c b/fs/reiserfs/stree.c
index 6b025a4..5fa7118 100644
--- a/fs/reiserfs/stree.c
+++ b/fs/reiserfs/stree.c
@@ -222,9 +222,6 @@ static inline int bin_search(const void *key, /* Key to search for. */
return ITEM_NOT_FOUND;
}
-#ifdef CONFIG_REISERFS_CHECK
-extern struct tree_balance *cur_tb;
-#endif
/* Minimal possible key. It is never in the tree. */
const struct reiserfs_key MIN_KEY = { 0, 0, {{0, 0},} };
@@ -711,7 +708,7 @@ int search_by_key(struct super_block *sb, const struct cpu_key *key, /* Key to s
!key_in_buffer(search_path, key, sb),
"PAP-5130: key is not in the buffer");
#ifdef CONFIG_REISERFS_CHECK
- if (cur_tb) {
+ if (REISERFS_SB(sb)->cur_tb) {
print_cur_tb("5140");
reiserfs_panic(sb, "PAP-5140",
"schedule occurred in do_balance!");
diff --git a/include/linux/reiserfs_fs_sb.h b/include/linux/reiserfs_fs_sb.h
index 8a1d409..2f8bb04 100644
--- a/include/linux/reiserfs_fs_sb.h
+++ b/include/linux/reiserfs_fs_sb.h
@@ -417,6 +417,17 @@ struct reiserfs_sb_info {
char *s_qf_names[MAXQUOTAS];
int s_jquota_fmt;
#endif
+#ifdef CONFIG_REISERFS_CHECK
+
+ struct tree_balance *cur_tb; /*
+ * Detects whether more than one
+ * copy of tb exists per superblock
+ * as a means of checking whether
+ * do_balance is executing concurrently
+ * against another tree reader/writer
+ * on a same mount point.
+ */
+#endif
};
/* Definitions of reiserfs on-disk properties: */
--
1.6.2.3
--
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