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author | Frederic Weisbecker <fweisbec@gmail.com> | 2009-05-16 19:10:38 +0200 |
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committer | Frederic Weisbecker <fweisbec@gmail.com> | 2009-09-14 07:18:25 +0200 |
commit | 08f14fc8963e585e65b71212ce8050607b9b6c36 (patch) | |
tree | 04d808f71193df2a90d485fcc0e2604bd8fe8d93 /fs/reiserfs/do_balan.c | |
parent | c72e05756b900b3be24cd73a16de52bab80984c0 (diff) | |
download | linux-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.c | 17 |
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 |