Re: [PATCH -mm] swsusp: Freeze filesystems during suspend (rev. 2)

Rafael J. Wysocki
2006-11-01T20:31:40Z

On Wednesday, 1 November 2006 20:54, Andrew Morton wrote:
> On Wed, 1 Nov 2006 18:53:07 +0100
> "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
>
> > +void freeze_filesystems(void)
> > +{
> > + struct super_block *sb;
> > +
> > + lockdep_off();
> > + /*
> > + * Freeze in reverse order so filesystems dependant upon others are
> > + * frozen in the right order (eg. loopback on ext3).
> > + */
> > + list_for_each_entry_reverse(sb, &super_blocks, s_list) {
> > + if (!sb->s_root || !sb->s_bdev ||
> > + (sb->s_frozen == SB_FREEZE_TRANS) ||
> > + (sb->s_flags & MS_RDONLY) ||
> > + (sb->s_flags & MS_FROZEN))
> > + continue;
> > +
> > + freeze_bdev(sb->s_bdev);
> > + sb->s_flags |= MS_FROZEN;
> > + }
> > + lockdep_on();
> > +}
> > +
> > +/**
> > + * thaw_filesystems - unlock all filesystems
> > + */
> > +void thaw_filesystems(void)
> > +{
> > + struct super_block *sb;
> > +
> > + lockdep_off();
> > +
> > + list_for_each_entry(sb, &super_blocks, s_list)
> > + if (sb->s_flags & MS_FROZEN) {
> > + sb->s_flags &= ~MS_FROZEN;
> > + thaw_bdev(sb->s_bdev, sb);
> > + }
> > +
> > + lockdep_on();
> > +}
>
> argh.
>
> The uncommented, unchangelogged lockdep_off() calls are completely
> mysterious right now, even before the patch is merged. They will not
> become less mysterious over time.

Of course. Sorry.

> Please, take pity upon the readers of your code. Add a comment.

OK (on top of the previous patch)

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
fs/buffer.c | 9 +++++++++
1 file changed, 9 insertions(+)

Index: linux-2.6.19-rc4-mm1/fs/buffer.c
===================================================================
--- linux-2.6.19-rc4-mm1.orig/fs/buffer.c
+++ linux-2.6.19-rc4-mm1/fs/buffer.c
@@ -252,6 +252,11 @@ void freeze_filesystems(void)
{
struct super_block *sb;

+ /*
+ * We are going to take several locks of the same class in a row
+ * without releasing them until thaw_filesystems() is called and
+ * lockdep won't know this is all OK.
+ */
lockdep_off();
/*
* Freeze in reverse order so filesystems dependant upon others are
@@ -277,6 +282,10 @@ void thaw_filesystems(void)
{
struct super_block *sb;

+ /*
+ * We are going to release several locks of the same class in a row
+ * and lockdep would complain about it, unnecessarily.
+ */
lockdep_off();

list_for_each_entry(sb, &super_blocks, s_list)