Skip to content

L
linux
Switch branch/tag
  1. 17 Apr, 2008 2 commits
    • Josef Bacik's avatar
      jbd2: fix possible journal overflow issues · 1dfc3220
      Josef Bacik authored 
      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: <linux-ext4@vger.kernel.org>
Cc: Jan Kara <jack@ucw.cz>
Signed-off-by: default avatarJosef Bacik <jbacik@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
      1dfc3220
    • Josef Bacik's avatar
      jbd2: fix the way the b_modified flag is cleared · 9fc7c63a
      Josef Bacik authored 
      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: <linux-ext4@vger.kernel.org>
Cc: Jan Kara <jack@ucw.cz>
Signed-off-by: default avatarJosef Bacik <jbacik@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
      9fc7c63a
  3. 29 Apr, 2008 38 commits
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7