jbd2: don't use state lock during commit path

Variables journal->j_fc_off, journal->j_fc_wbuf are accessed during
commit path. Since today we allow only one process to perform a fast
commit, there is no need take state lock before accessing these
variables. This patch removes these locks and adds comments to
describe this.

Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20201106035911.1942128-9-harshadshirwadkar@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 500152f0421a5e0e4207401e5e0ce1b9c0a84c10..778ea50fc8d11edfccf6614240bd508aeffeff7e 100644 (file)
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -865,7 +865,6 @@ int jbd2_fc_get_buf(journal_t *journal, struct buffer_head **bh_out)
        int fc_off;
 
        *bh_out = NULL;
-       write_lock(&journal->j_state_lock);
 
        if (journal->j_fc_off + journal->j_fc_first < journal->j_fc_last) {
                fc_off = journal->j_fc_off;
@@ -874,7 +873,6 @@ int jbd2_fc_get_buf(journal_t *journal, struct buffer_head **bh_out)
        } else {
                ret = -EINVAL;
        }
-       write_unlock(&journal->j_state_lock);
 
        if (ret)
                return ret;
@@ -909,9 +907,7 @@ int jbd2_fc_wait_bufs(journal_t *journal, int num_blks)
        struct buffer_head *bh;
        int i, j_fc_off;
 
-       read_lock(&journal->j_state_lock);
        j_fc_off = journal->j_fc_off;
-       read_unlock(&journal->j_state_lock);
 
        /*
         * Wait in reverse order to minimize chances of us being woken up before
@@ -939,9 +935,7 @@ int jbd2_fc_release_bufs(journal_t *journal)
        struct buffer_head *bh;
        int i, j_fc_off;
 
-       read_lock(&journal->j_state_lock);
        j_fc_off = journal->j_fc_off;
-       read_unlock(&journal->j_state_lock);
 
        /*
         * Wait in reverse order to minimize chances of us being woken up before

diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index b2caf7bbd8e568cca1e4cd4ba334fef80d6d57cd..5f0ef6380b0c8ba750b717b284ec04b77ae95fa1 100644 (file)
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -945,8 +945,9 @@ struct journal_s
        /**
         * @j_fc_off:
         *
-        * Number of fast commit blocks currently allocated.
-        * [j_state_lock].
+        * Number of fast commit blocks currently allocated. Accessed only
+        * during fast commit. Currently only process can do fast commit, so
+        * this field is not protected by any lock.
         */
        unsigned long           j_fc_off;
 
@@ -1109,8 +1110,9 @@ struct journal_s
        struct buffer_head      **j_wbuf;
 
        /**
-        * @j_fc_wbuf: Array of fast commit bhs for
-        * jbd2_journal_commit_transaction.
+        * @j_fc_wbuf: Array of fast commit bhs for fast commit. Accessed only
+        * during a fast commit. Currently only process can do fast commit, so
+        * this field is not protected by any lock.
         */
        struct buffer_head      **j_fc_wbuf;