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author | Frederic Weisbecker <fweisbec@gmail.com> | 2009-05-16 17:10:38 (GMT) |
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committer | Frederic Weisbecker <fweisbec@gmail.com> | 2009-09-14 05:18:25 (GMT) |
commit | 08f14fc8963e585e65b71212ce8050607b9b6c36 (patch) | |
tree | 04d808f71193df2a90d485fcc0e2604bd8fe8d93 /include/linux/reiserfs_fs_sb.h | |
parent | c72e05756b900b3be24cd73a16de52bab80984c0 (diff) | |
download | linux-fsl-qoriq-08f14fc8963e585e65b71212ce8050607b9b6c36.tar.xz |
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 'include/linux/reiserfs_fs_sb.h')
-rw-r--r-- | include/linux/reiserfs_fs_sb.h | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/include/linux/reiserfs_fs_sb.h b/include/linux/reiserfs_fs_sb.h index 045c372..52c83b6 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: */ |