From 9fc7c63a1d6e9920038ced782390a54888ed70a6 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Thu, 17 Apr 2008 10:38:59 -0400 Subject: jbd2: fix the way the b_modified flag is cleared Currently at the start of a journal commit we loop through all of the buffers on the committing transaction and clear the b_modified flag (the flag that is set when a transaction modifies the buffer) under the j_list_lock. The problem is that everywhere else this flag is modified only under the jbd2 lock buffer flag, so it will race with a running transaction who could potentially set it, and have it unset by the committing transaction. This is also a big waste, you can have several thousands of buffers that you are clearing the modified flag on when you may not need to. This patch removes this code and instead clears the b_modified flag upon entering do_get_write_access/journal_get_create_access, so if that transaction does indeed use the buffer then it will be accounted for properly, and if it does not then we know we didn't use it. That will be important for the next patch in this series. Tested thoroughly by myself using postmark/iozone/bonnie++. Cc: Cc: Jan Kara Signed-off-by: Josef Bacik Signed-off-by: Andrew Morton Signed-off-by: "Theodore Ts'o" --- fs/jbd2/commit.c | 16 ---------------- 1 file changed, 16 deletions(-) (limited to 'fs/jbd2/commit.c') diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c index a8173081f831..988fbec1143c 100644 --- a/fs/jbd2/commit.c +++ b/fs/jbd2/commit.c @@ -519,22 +519,6 @@ void jbd2_journal_commit_transaction(journal_t *journal) jbd_debug (3, "JBD: commit phase 2\n"); - /* - * First, drop modified flag: all accesses to the buffers - * will be tracked for a new trasaction only -bzzz - */ - spin_lock(&journal->j_list_lock); - if (commit_transaction->t_buffers) { - new_jh = jh = commit_transaction->t_buffers->b_tnext; - do { - J_ASSERT_JH(new_jh, new_jh->b_modified == 1 || - new_jh->b_modified == 0); - new_jh->b_modified = 0; - new_jh = new_jh->b_tnext; - } while (new_jh != jh); - } - spin_unlock(&journal->j_list_lock); - /* * Now start flushing things to disk, in the order they appear * on the transaction lists. Data blocks go first. -- cgit v1.2.2 From 1dfc3220d963385a317264b11154c462a83596ed Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Thu, 17 Apr 2008 10:38:59 -0400 Subject: jbd2: fix possible journal overflow issues There are several cases where the running transaction can get buffers added to its BJ_Metadata list which it never dirtied, which makes its t_nr_buffers counter end up larger than its t_outstanding_credits counter. This will cause issues when starting new transactions as while we are logging buffers we decrement t_outstanding_buffers, so when t_outstanding_buffers goes negative, we will report that we need less space in the journal than we actually need, so transactions will be started even though there may not be enough room for them. In the worst case scenario (which admittedly is almost impossible to reproduce) this will result in the journal running out of space. The fix is to only refile buffers from the committing transaction to the running transactions BJ_Modified list when b_modified is set on that journal, which is the only way to be sure if the running transaction has modified that buffer. This patch also fixes an accounting error in journal_forget, it is possible that we can call journal_forget on a buffer without having modified it, only gotten write access to it, so instead of freeing a credit, we only do so if the buffer was modified. The assert will help catch if this problem occurs. Without these two patches I could hit this assert within minutes of running postmark, with them this issue no longer arises. Cc: Cc: Jan Kara Signed-off-by: Josef Bacik Signed-off-by: Andrew Morton Signed-off-by: "Theodore Ts'o" --- fs/jbd2/commit.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'fs/jbd2/commit.c') diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c index 988fbec1143c..e0139786f717 100644 --- a/fs/jbd2/commit.c +++ b/fs/jbd2/commit.c @@ -568,6 +568,9 @@ void jbd2_journal_commit_transaction(journal_t *journal) stats.u.run.rs_blocks = commit_transaction->t_outstanding_credits; stats.u.run.rs_blocks_logged = 0; + J_ASSERT(commit_transaction->t_nr_buffers <= + commit_transaction->t_outstanding_credits); + descriptor = NULL; bufs = 0; while (commit_transaction->t_buffers) { -- cgit v1.2.2