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authorJan Kara <jack@suse.cz>2009-04-14 01:40:06 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2009-04-14 02:04:32 +0400
commit32433879480d13bc019d5a067ce884064a93dd63 (patch)
tree652230bb84c0d93d06b8ed17049e9a8229283907 /fs/jbd
parent9de100d001564f58c3fb2ec1bd03e540ac0aa357 (diff)
downloadlinux-32433879480d13bc019d5a067ce884064a93dd63.tar.xz
jbd: update locking coments
Update information about locking in JBD revoke code. Reported-by: Lin Tan <tammy000@gmail.com>. Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/jbd')
-rw-r--r--fs/jbd/revoke.c24
1 files changed, 19 insertions, 5 deletions
diff --git a/fs/jbd/revoke.c b/fs/jbd/revoke.c
index c7bd649bbbdc..3e9afc2a91d2 100644
--- a/fs/jbd/revoke.c
+++ b/fs/jbd/revoke.c
@@ -55,6 +55,25 @@
* need do nothing.
* RevokeValid set, Revoked set:
* buffer has been revoked.
+ *
+ * Locking rules:
+ * We keep two hash tables of revoke records. One hashtable belongs to the
+ * running transaction (is pointed to by journal->j_revoke), the other one
+ * belongs to the committing transaction. Accesses to the second hash table
+ * happen only from the kjournald and no other thread touches this table. Also
+ * journal_switch_revoke_table() which switches which hashtable belongs to the
+ * running and which to the committing transaction is called only from
+ * kjournald. Therefore we need no locks when accessing the hashtable belonging
+ * to the committing transaction.
+ *
+ * All users operating on the hash table belonging to the running transaction
+ * have a handle to the transaction. Therefore they are safe from kjournald
+ * switching hash tables under them. For operations on the lists of entries in
+ * the hash table j_revoke_lock is used.
+ *
+ * Finally, also replay code uses the hash tables but at this moment noone else
+ * can touch them (filesystem isn't mounted yet) and hence no locking is
+ * needed.
*/
#ifndef __KERNEL__
@@ -402,8 +421,6 @@ int journal_revoke(handle_t *handle, unsigned long blocknr,
* the second time we would still have a pending revoke to cancel. So,
* do not trust the Revoked bit on buffers unless RevokeValid is also
* set.
- *
- * The caller must have the journal locked.
*/
int journal_cancel_revoke(handle_t *handle, struct journal_head *jh)
{
@@ -481,10 +498,7 @@ void journal_switch_revoke_table(journal_t *journal)
/*
* Write revoke records to the journal for all entries in the current
* revoke hash, deleting the entries as we go.
- *
- * Called with the journal lock held.
*/
-
void journal_write_revoke_records(journal_t *journal,
transaction_t *transaction)
{