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SubjectRe: [PATCH 5/5] ext2: Add ext2_sb_info s_lock spinlock
On Tue, Apr 13, Jan Kara wrote:

> On Mon 12-04-10 22:41:45, Jan Blunck wrote:
> > Add a spinlock that protects against concurrent modifications of
> > s_mount_state, s_blocks_last, s_overhead_last and the content of the
> > superblock's buffer pointed to by sbi->s_es. This is a preparation patch
> > for removing the BKL from ext2 in the next patch.
> >
> > Signed-off-by: Jan Blunck <jblunck@suse.de>
> > Cc: Andi Kleen <andi@firstfloor.org>
> > Cc: Jan Kara <jack@suse.cz>
> > Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
> > ---
> > fs/ext2/inode.c | 2 ++
> > fs/ext2/super.c | 31 +++++++++++++++++++++++++++++--
> > include/linux/ext2_fs_sb.h | 6 ++++++
> > 3 files changed, 37 insertions(+), 2 deletions(-)
> >
> >diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> >index fc13cc1..5d15442 100644
> >--- a/fs/ext2/inode.c
> >+++ b/fs/ext2/inode.c
> >@@ -1407,9 +1407,11 @@ static int __ext2_write_inode(struct inode *inode, int do_sync)
> > * created, add a flag to the superblock.
> > */
> > lock_kernel();
> >+ spin_lock(&EXT2_SB(sb)->s_lock);
> > ext2_update_dynamic_rev(sb);
> > EXT2_SET_RO_COMPAT_FEATURE(sb,
> > EXT2_FEATURE_RO_COMPAT_LARGE_FILE);
> >+ spin_unlock(&EXT2_SB(sb)->s_lock);
> > unlock_kernel();
> > ext2_write_super(sb);
> > }
> Looking at this - probably we should protect by this lock also setting of
> a feature in ext2_xattr_update_super_block(). It's an unrelated bugfix but
> when we are already doing the bugfixing & cleanups in this area...
>
> > diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> > index b01c491..34d7a62 100644
> > --- a/fs/ext2/super.c
> > +++ b/fs/ext2/super.c
> > @@ -209,6 +216,7 @@ static int ext2_show_options(struct seq_file *seq, struct vfsmount *vfs)
> > struct ext2_super_block *es = sbi->s_es;
> > unsigned long def_mount_opts;
> >
> > + spin_lock(&sbi->s_lock);
> > def_mount_opts = le32_to_cpu(es->s_default_mount_opts);
> >
> > if (sbi->s_sb_block != 1)
> > @@ -281,6 +289,7 @@ static int ext2_show_options(struct seq_file *seq, struct vfsmount *vfs)
> > if (!test_opt(sb, RESERVATION))
> > seq_puts(seq, ",noreservation");
> >
> > + spin_unlock(&sbi->s_lock);
> > return 0;
> > }
> Why exactly do you have in the above? Probably because of consistent
> view of mount options? You should comment about that in the changelo and
> especially at the lock declaration in ext2_fs.h.
>
> > @@ -1158,19 +1173,22 @@ static void ext2_sync_super(struct super_block *sb, struct ext2_super_block *es)
> > * may have been checked while mounted and e2fsck may have
> > * set s_state to EXT2_VALID_FS after some corrections.
> > */
> > -
> > static int ext2_sync_fs(struct super_block *sb, int wait)
> > {
> > + struct ext2_sb_info *sbi = EXT2_SB(sb);
> > struct ext2_super_block *es = EXT2_SB(sb)->s_es;
> > struct buffer_head *sbh = EXT2_SB(sb)->s_sbh;
> >
> > lock_kernel();
> > + spin_lock(&sbi->s_lock);
> > if (es->s_state & cpu_to_le16(EXT2_VALID_FS)) {
> > ext2_debug("setting valid to 0\n");
> > es->s_state &= cpu_to_le16(~EXT2_VALID_FS);
> > + spin_unlock(&sbi->s_lock);
> > ext2_sync_super(sb, es);
> > } else {
> > ext2_commit_super(sb, es);
> > + spin_unlock(&sbi->s_lock);
> Could you please fold in ext2_commit_super? It's used only here and it's
> name looks a bit scary to be called under the spinlock...

Right. Is there actually a reason why we don't update the s_free_blocks_count
and s_free_inodes_count when we found the filesystem did not have the
EXT2_VALID_FS set? Otherwise I could use ext2_sync_super() in both and make it
honor the wait flag by just calling sync_dirty_buffer() when it is necessary.

What do you think?

diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 40fc8d5..8187061 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -39,7 +39,7 @@
#include "xip.h"

static void ext2_sync_super(struct super_block *sb,
- struct ext2_super_block *es);
+ struct ext2_super_block *es, int wait);
static int ext2_remount (struct super_block * sb, int * flags, char * data);
static int ext2_statfs (struct dentry * dentry, struct kstatfs * buf);
static int ext2_sync_fs(struct super_block *sb, int wait);
@@ -54,7 +54,7 @@ void ext2_error (struct super_block * sb, const char * function,
if (!(sb->s_flags & MS_RDONLY)) {
sbi->s_mount_state |= EXT2_ERROR_FS;
es->s_state |= cpu_to_le16(EXT2_ERROR_FS);
- ext2_sync_super(sb, es);
+ ext2_sync_super(sb, es, 1);
}

va_start(args, fmt);
@@ -125,7 +125,7 @@ static void ext2_put_super (struct super_block * sb)
struct ext2_super_block *es = sbi->s_es;

es->s_state = cpu_to_le16(sbi->s_mount_state);
- ext2_sync_super(sb, es);
+ ext2_sync_super(sb, es, 1);
}
db_count = sbi->s_gdb_count;
for (i = 0; i < db_count; i++)
@@ -1127,23 +1127,16 @@ static void ext2_clear_super_error(struct super_block *sb)
}
}

-static void ext2_commit_super (struct super_block * sb,
- struct ext2_super_block * es)
-{
- ext2_clear_super_error(sb);
- es->s_wtime = cpu_to_le32(get_seconds());
- mark_buffer_dirty(EXT2_SB(sb)->s_sbh);
- sb->s_dirt = 0;
-}
-
-static void ext2_sync_super(struct super_block *sb, struct ext2_super_block *es)
+static void ext2_sync_super(struct super_block *sb, struct ext2_super_block *es,
+ int wait)
{
ext2_clear_super_error(sb);
es->s_free_blocks_count = cpu_to_le32(ext2_count_free_blocks(sb));
es->s_free_inodes_count = cpu_to_le32(ext2_count_free_inodes(sb));
es->s_wtime = cpu_to_le32(get_seconds());
mark_buffer_dirty(EXT2_SB(sb)->s_sbh);
- sync_dirty_buffer(EXT2_SB(sb)->s_sbh);
+ if (wait)
+ sync_dirty_buffer(EXT2_SB(sb)->s_sbh);
sb->s_dirt = 0;
}

@@ -1167,11 +1160,8 @@ static int ext2_sync_fs(struct super_block *sb, int wait)
if (es->s_state & cpu_to_le16(EXT2_VALID_FS)) {
ext2_debug("setting valid to 0\n");
es->s_state &= cpu_to_le16(~EXT2_VALID_FS);
- ext2_sync_super(sb, es);
- } else {
- ext2_commit_super(sb, es);
}
- sb->s_dirt = 0;
+ ext2_sync_super(sb, es, wait);
unlock_kernel();

return 0;
@@ -1269,7 +1259,7 @@ static int ext2_remount (struct super_block * sb, int * flags, char * data)
if (!ext2_setup_super (sb, es, 0))
sb->s_flags &= ~MS_RDONLY;
}
- ext2_sync_super(sb, es);
+ ext2_sync_super(sb, es, 1);
unlock_kernel();
return 0;
restore_opts:

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