On Fri 05-10-12 14:31:46, Fernando Luis Vázquez Cao wrote:
> iterate_supers() calls a function provided by the caller with the s_umount
> semaphore taken in read mode. However, there may be cases where write mode
> is preferable, so we add __iterate_supers(), which lets one
> specify the mode of the lock, and replace iterate_supers with two helpers
> around __iterate_supers(), iterate_supers_read() and iterate_supers_write().
>
> This will be used to fix the emergency thaw (filesystem unfreeze) code, which
> iterates over the list of superblocks but needs to hold the s_umount semaphore
> in _write_ mode bebore carrying out the actual thaw operation.
>
> This patch introduces no semantic changes since current iterate_supers()
> callers are just updated to use iterate_supers_read() instead.
The patch looks good. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
>
> Cc: Josef Bacik <jbacik@xxxxxxxxxxxx>
> Cc: Eric Sandeen <sandeen@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Dave Chinner <dchinner@xxxxxxxxxx>
> Signed-off-by: Fernando Luis Vazquez Cao <fernando@xxxxxxxxxxxxx>
> ---
>
> diff -urNp linux-3.6.0-rc7-orig/fs/buffer.c linux-3.6.0-rc7/fs/buffer.c
> --- linux-3.6.0-rc7-orig/fs/buffer.c 2012-09-24 13:45:05.569520902 +0900
> +++ linux-3.6.0-rc7/fs/buffer.c 2012-09-26 13:06:06.578342989 +0900
> @@ -521,7 +521,7 @@ static void do_thaw_one(struct super_blo
>
> static void do_thaw_all(struct work_struct *work)
> {
> - iterate_supers(do_thaw_one, NULL);
> + iterate_supers_read(do_thaw_one, NULL);
> kfree(work);
> printk(KERN_WARNING "Emergency Thaw complete\n");
> }
> diff -urNp linux-3.6.0-rc7-orig/fs/drop_caches.c linux-3.6.0-rc7/fs/drop_caches.c
> --- linux-3.6.0-rc7-orig/fs/drop_caches.c 2012-07-22 05:58:29.000000000 +0900
> +++ linux-3.6.0-rc7/fs/drop_caches.c 2012-09-26 13:06:06.582342990 +0900
> @@ -59,7 +59,7 @@ int drop_caches_sysctl_handler(ctl_table
> return ret;
> if (write) {
> if (sysctl_drop_caches & 1)
> - iterate_supers(drop_pagecache_sb, NULL);
> + iterate_supers_read(drop_pagecache_sb, NULL);
> if (sysctl_drop_caches & 2)
> drop_slab();
> }
> diff -urNp linux-3.6.0-rc7-orig/fs/quota/quota.c linux-3.6.0-rc7/fs/quota/quota.c
> --- linux-3.6.0-rc7-orig/fs/quota/quota.c 2012-09-24 13:45:06.105520990 +0900
> +++ linux-3.6.0-rc7/fs/quota/quota.c 2012-09-26 13:06:06.594342992 +0900
> @@ -58,7 +58,7 @@ static int quota_sync_all(int type)
> return -EINVAL;
> ret = security_quotactl(Q_SYNC, type, 0, NULL);
> if (!ret)
> - iterate_supers(quota_sync_one, &type);
> + iterate_supers_read(quota_sync_one, &type);
> return ret;
> }
>
> diff -urNp linux-3.6.0-rc7-orig/fs/super.c linux-3.6.0-rc7/fs/super.c
> --- linux-3.6.0-rc7-orig/fs/super.c 2012-09-24 13:45:06.129520994 +0900
> +++ linux-3.6.0-rc7/fs/super.c 2012-09-26 13:14:39.462346665 +0900
> @@ -537,14 +537,16 @@ void drop_super(struct super_block *sb)
> EXPORT_SYMBOL(drop_super);
>
> /**
> - * iterate_supers - call function for all active superblocks
> + * __iterate_supers - call function for all active superblocks
> * @f: function to call
> * @arg: argument to pass to it
> + * @wlock: mode of superblock lock (false->read lock, true->write lock)
> *
> * Scans the superblock list and calls given function, passing it
> * locked superblock and given argument.
> */
> -void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
> +static void __iterate_supers(void (*f)(struct super_block *, void *), void *arg,
> + bool wlock)
> {
> struct super_block *sb, *p = NULL;
>
> @@ -555,10 +557,18 @@ void iterate_supers(void (*f)(struct sup
> sb->s_count++;
> spin_unlock(&sb_lock);
>
> - down_read(&sb->s_umount);
> + if (wlock)
> + down_write(&sb->s_umount);
> + else
> + down_read(&sb->s_umount);
> +
> if (sb->s_root && (sb->s_flags & MS_BORN))
> f(sb, arg);
> - up_read(&sb->s_umount);
> +
> + if (wlock)
> + up_write(&sb->s_umount);
> + else
> + up_read(&sb->s_umount);
>
> spin_lock(&sb_lock);
> if (p)
> @@ -571,6 +581,34 @@ void iterate_supers(void (*f)(struct sup
> }
>
> /**
> + * iterate_supers_read - call function for all active superblocks
> + * @f: function to call
> + * @arg: argument to pass to it
> + *
> + * Scans the superblock list and calls given function, passing it
> + * a superblock locked in _read_ mode and given argument. The lock
> + * is automatically relased after the function returns.
> + */
> +void iterate_supers_read(void (*f)(struct super_block *, void *), void *arg)
> +{
> + __iterate_supers(f, arg , false);
> +}
> +
> +/**
> + * iterate_supers_write - call function for all active superblocks
> + * @f: function to call
> + * @arg: argument to pass to it
> + *
> + * Scans the superblock list and calls given function, passing it
> + * a superblock locked in _write_ mode and given argument. The lock
> + * is automatically relased after the function returns.
> + */
> +void iterate_supers_write(void (*f)(struct super_block *, void *), void *arg)
> +{
> + __iterate_supers(f, arg , true);
> +}
> +
> +/**
> * iterate_supers_type - call function for superblocks of given type
> * @type: fs type
> * @f: function to call
> diff -urNp linux-3.6.0-rc7-orig/fs/sync.c linux-3.6.0-rc7/fs/sync.c
> --- linux-3.6.0-rc7-orig/fs/sync.c 2012-09-24 13:45:06.129520994 +0900
> +++ linux-3.6.0-rc7/fs/sync.c 2012-09-26 13:06:06.594342992 +0900
> @@ -104,9 +104,9 @@ SYSCALL_DEFINE0(sync)
> int nowait = 0, wait = 1;
>
> wakeup_flusher_threads(0, WB_REASON_SYNC);
> - iterate_supers(sync_inodes_one_sb, NULL);
> - iterate_supers(sync_fs_one_sb, &nowait);
> - iterate_supers(sync_fs_one_sb, &wait);
> + iterate_supers_read(sync_inodes_one_sb, NULL);
> + iterate_supers_read(sync_fs_one_sb, &nowait);
> + iterate_supers_read(sync_fs_one_sb, &wait);
> iterate_bdevs(fdatawrite_one_bdev, NULL);
> iterate_bdevs(fdatawait_one_bdev, NULL);
> if (unlikely(laptop_mode))
> @@ -122,11 +122,11 @@ static void do_sync_work(struct work_str
> * Sync twice to reduce the possibility we skipped some inodes / pages
> * because they were temporarily locked
> */
> - iterate_supers(sync_inodes_one_sb, &nowait);
> - iterate_supers(sync_fs_one_sb, &nowait);
> + iterate_supers_read(sync_inodes_one_sb, &nowait);
> + iterate_supers_read(sync_fs_one_sb, &nowait);
> iterate_bdevs(fdatawrite_one_bdev, NULL);
> - iterate_supers(sync_inodes_one_sb, &nowait);
> - iterate_supers(sync_fs_one_sb, &nowait);
> + iterate_supers_read(sync_inodes_one_sb, &nowait);
> + iterate_supers_read(sync_fs_one_sb, &nowait);
> iterate_bdevs(fdatawrite_one_bdev, NULL);
> printk("Emergency Sync complete\n");
> kfree(work);
> diff -urNp linux-3.6.0-rc7-orig/include/linux/fs.h linux-3.6.0-rc7/include/linux/fs.h
> --- linux-3.6.0-rc7-orig/include/linux/fs.h 2012-09-24 13:45:06.301521033 +0900
> +++ linux-3.6.0-rc7/include/linux/fs.h 2012-09-26 13:06:06.598342993 +0900
> @@ -2684,7 +2684,8 @@ extern struct super_block *get_super(str
> extern struct super_block *get_super_thawed(struct block_device *);
> extern struct super_block *get_active_super(struct block_device *bdev);
> extern void drop_super(struct super_block *sb);
> -extern void iterate_supers(void (*)(struct super_block *, void *), void *);
> +extern void iterate_supers_read(void (*)(struct super_block *, void *), void *);
> +extern void iterate_supers_write(void (*)(struct super_block *, void *), void *);
> extern void iterate_supers_type(struct file_system_type *,
> void (*)(struct super_block *, void *), void *);
>
> diff -urNp linux-3.6.0-rc7-orig/security/selinux/hooks.c linux-3.6.0-rc7/security/selinux/hooks.c
> --- linux-3.6.0-rc7-orig/security/selinux/hooks.c 2012-09-24 13:45:08.121521275 +0900
> +++ linux-3.6.0-rc7/security/selinux/hooks.c 2012-09-26 13:06:06.610342995 +0900
> @@ -5755,7 +5755,7 @@ void selinux_complete_init(void)
>
> /* Set up any superblocks initialized prior to the policy load. */
> printk(KERN_DEBUG "SELinux: Setting up existing superblocks.\n");
> - iterate_supers(delayed_superblock_init, NULL);
> + iterate_supers_read(delayed_superblock_init, NULL);
> }
>
> /* SELinux requires early initialization in order to label
>
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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