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jbd2: Update locking coments

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Update information about locking in JBD2 revoke code. Inconsistency in
comments found by Lin Tan <tammy000@gmail.com>.

CC: Lin Tan <tammy000@gmail.com>.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Jan Kara 2009-03-27 17:20:40 -04:00 committed by Theodore Ts'o
parent cc0fb9ad7d
commit 86db97c87f
1 changed files with 19 additions and 5 deletions
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24
fs/jbd2/revoke.c
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@ -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* buffer has been revoked.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__
@ -401,8 +420,6 @@ int jbd2_journal_revoke(handle_t *handle, unsigned long 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 jbd2_journal_cancel_revoke(handle_t *handle, struct journal_head *jh)
{
@ -480,10 +497,7 @@ void jbd2_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 jbd2_journal_write_revoke_records(journal_t *journal,
transaction_t *transaction)
{