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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>
This commit is contained in:
Jan Kara 2009-04-13 14:40:06 -07:00 committed by Linus Torvalds
parent 9de100d001
commit 3243387948
1 changed files with 19 additions and 5 deletions
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24
fs/jbd/revoke.c
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@ -55,6 +55,25 @@
* need do nothing. * need do nothing.
* RevokeValid set, Revoked set: * RevokeValid set, Revoked set:
* buffer has been revoked. * buffer has been revoked.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__ #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, * 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 * do not trust the Revoked bit on buffers unless RevokeValid is also
* set. * set.
*
* The caller must have the journal locked.
*/ */
int journal_cancel_revoke(handle_t *handle, struct journal_head *jh) 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 * Write revoke records to the journal for all entries in the current
* revoke hash, deleting the entries as we go. * revoke hash, deleting the entries as we go.
*
* Called with the journal lock held.
*/ */
void journal_write_revoke_records(journal_t *journal, void journal_write_revoke_records(journal_t *journal,
transaction_t *transaction) transaction_t *transaction)
{ {