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kill-the-bkl/reiserfs: move the concurrent tree accesses checks per superblock

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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>
This commit is contained in:
Frederic Weisbecker
2009-05-16 19:10:38 +02:00
parent c72e05756b
commit 08f14fc896
5 changed files with 18 additions and 24 deletions
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17
fs/reiserfs/do_balan.c
View File

@@ -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