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Date: Thu, 5 Nov 2009 14:06:35 +0100
From: Jan Blunck <jblunck@...e.de>
To: Jan Kara <jack@...e.cz>
Cc: linux-fsdevel@...r.kernel.org, Matthew Wilcox <matthew@....cx>,
linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
Al Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Andi Kleen <ak@...ux.intel.com>,
Christoph Hellwig <hch@....de>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 05/27] BKL: Remove BKL from ext2 filesystem
On Thu, Nov 05, Jan Kara wrote:
> On Mon 02-11-09 11:04:45, Jan Blunck wrote:
> > The BKL is still used in ext2_put_super(), ext2_fill_super(), ext2_sync_fs()
> > ext2_remount() and ext2_write_inode(). From these calls ext2_put_super(),
> > ext2_fill_super() and ext2_remount() are protected against each other by
> > the struct super_block s_umount rw semaphore. The call in ext2_write_inode()
> > could only protect the modification of the ext2_sb_info through
> > ext2_update_dynamic_rev() against concurrent ext2_sync_fs() or ext2_remount().
> > ext2_fill_super() and ext2_put_super() can be left out because you need a
> > valid filesystem reference in all three cases, which you do not have when
> > you are one of these functions.
> This is not quite true. Actually, ext2_sync_fs() is called also with
> s_umount held (for reading) so it cannot race with any of the mounting /
> umounting functions. But it should probably be guarded against running two
> instances of ext2_sync_fs() in parallel.
> Looking into the code, we probably have a race in ext2_write_inode that
> two threads can write one inode in parallel. But that's a separe issue from
> BKL removal.
Have you actually seen that the previous patch introduces s_mutex? Meanwhile
that mutex has been replaced by a spinlock due to Andy's feedback.
Anyway, thanks for the review.
Cheers,
Jan
> Honza
>
> > diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> > index 057074e..8b51416 100644
> > --- a/fs/ext2/inode.c
> > +++ b/fs/ext2/inode.c
> > @@ -22,7 +22,6 @@
> > * Assorted race fixes, rewrite of ext2_get_block() by Al Viro, 2000
> > */
> >
> > -#include <linux/smp_lock.h>
> > #include <linux/time.h>
> > #include <linux/highuid.h>
> > #include <linux/pagemap.h>
> > @@ -1400,13 +1399,11 @@ int ext2_write_inode(struct inode *inode, int do_sync)
> > /* If this is the first large file
> > * created, add a flag to the superblock.
> > */
> > - lock_kernel();
> > mutex_lock(&EXT2_SB(sb)->s_mutex);
> > ext2_update_dynamic_rev(sb);
> > EXT2_SET_RO_COMPAT_FEATURE(sb,
> > EXT2_FEATURE_RO_COMPAT_LARGE_FILE);
> > mutex_unlock(&EXT2_SB(sb)->s_mutex);
> > - unlock_kernel();
> > ext2_write_super(sb);
> > }
> > }
> > diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> > index d610eb9..7e819ac 100644
> > --- a/fs/ext2/super.c
> > +++ b/fs/ext2/super.c
> > @@ -26,7 +26,6 @@
> > #include <linux/random.h>
> > #include <linux/buffer_head.h>
> > #include <linux/exportfs.h>
> > -#include <linux/smp_lock.h>
> > #include <linux/vfs.h>
> > #include <linux/seq_file.h>
> > #include <linux/mount.h>
> > @@ -118,8 +117,6 @@ static void ext2_put_super (struct super_block * sb)
> > int i;
> > struct ext2_sb_info *sbi = EXT2_SB(sb);
> >
> > - lock_kernel();
> > -
> > if (sb->s_dirt && !(sb->s_flags & MS_RDONLY))
> > ext2_sync_fs(sb, 1);
> >
> > @@ -143,8 +140,6 @@ static void ext2_put_super (struct super_block * sb)
> > sb->s_fs_info = NULL;
> > kfree(sbi->s_blockgroup_lock);
> > kfree(sbi);
> > -
> > - unlock_kernel();
> > }
> >
> > static struct kmem_cache * ext2_inode_cachep;
> > @@ -750,8 +745,6 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
> > __le32 features;
> > int err;
> >
> > - lock_kernel();
> > -
> > err = -ENOMEM;
> > sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> > if (!sbi)
> > @@ -1077,7 +1070,6 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
> > ext2_warning(sb, __func__,
> > "mounting ext3 filesystem as ext2");
> > ext2_setup_super (sb, es, sb->s_flags & MS_RDONLY);
> > - unlock_kernel();
> > return 0;
> >
> > cantfind_ext2:
> > @@ -1102,7 +1094,6 @@ failed_sbi:
> > kfree(sbi->s_blockgroup_lock);
> > kfree(sbi);
> > failed_unlock:
> > - unlock_kernel();
> > return ret;
> > }
> >
> > @@ -1140,7 +1131,6 @@ static int ext2_sync_fs(struct super_block *sb, int wait)
> > {
> > struct ext2_super_block *es = EXT2_SB(sb)->s_es;
> >
> > - lock_kernel();
> > 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);
> > @@ -1154,7 +1144,6 @@ static int ext2_sync_fs(struct super_block *sb, int wait)
> > ext2_commit_super(sb, es);
> > }
> > sb->s_dirt = 0;
> > - unlock_kernel();
> >
> > return 0;
> > }
> > @@ -1181,7 +1170,6 @@ static int ext2_remount (struct super_block * sb, int * flags, char * data)
> > unsigned long old_sb_flags;
> > int err;
> >
> > - lock_kernel();
> > mutex_lock(&sbi->s_mutex);
> >
> > /* Store the old options */
> > @@ -1221,14 +1209,12 @@ static int ext2_remount (struct super_block * sb, int * flags, char * data)
> > }
> > if ((*flags & MS_RDONLY) == (sb->s_flags & MS_RDONLY)) {
> > mutex_unlock(&sbi->s_mutex);
> > - unlock_kernel();
> > return 0;
> > }
> > if (*flags & MS_RDONLY) {
> > if (le16_to_cpu(es->s_state) & EXT2_VALID_FS ||
> > !(sbi->s_mount_state & EXT2_VALID_FS)) {
> > mutex_unlock(&sbi->s_mutex);
> > - unlock_kernel();
> > return 0;
> > }
> > /*
> > @@ -1258,7 +1244,6 @@ static int ext2_remount (struct super_block * sb, int * flags, char * data)
> > }
> > ext2_sync_super(sb, es);
> > mutex_unlock(&sbi->s_mutex);
> > - unlock_kernel();
> > return 0;
> > restore_opts:
> > sbi->s_mount_opt = old_opts.s_mount_opt;
> > @@ -1266,7 +1251,6 @@ restore_opts:
> > sbi->s_resgid = old_opts.s_resgid;
> > sb->s_flags = old_sb_flags;
> > mutex_unlock(&sbi->s_mutex);
> > - unlock_kernel();
> > return err;
> > }
> >
> > --
> > 1.6.4.2
> >
> --
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR
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