From 8f82f840ec6ab873f520364d443ff6fa1b3f8e22 Mon Sep 17 00:00:00 2001 From: Yongqiang Yang Date: Tue, 26 Jul 2011 21:35:44 -0400 Subject: [PATCH] ext4: prevent parallel resizers by atomic bit ops Before this patch, parallel resizers are allowed and protected by a mutex lock, actually, there is no need to support parallel resizer, so this patch prevents parallel resizers by atmoic bit ops, like lock_page() and unlock_page() do. To do this, the patch removed the mutex lock s_resize_lock from struct ext4_sb_info and added a unsigned long field named s_resize_flags which inidicates if there is a resizer. Signed-off-by: Yongqiang Yang Signed-off-by: "Theodore Ts'o" --- fs/ext4/ext4.h | 7 ++++++- fs/ext4/ioctl.c | 12 ++++++++---- fs/ext4/resize.c | 55 +++++++++++++++++++++---------------------------------- fs/ext4/super.c | 2 +- 4 files changed, 36 insertions(+), 40 deletions(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 62cee2b..bb0f776 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1127,7 +1127,8 @@ struct ext4_sb_info { struct journal_s *s_journal; struct list_head s_orphan; struct mutex s_orphan_lock; - struct mutex s_resize_lock; + unsigned long s_resize_flags; /* Flags indicating if there + is a resizer */ unsigned long s_commit_interval; u32 s_max_batch_time; u32 s_min_batch_time; @@ -2269,6 +2270,10 @@ static inline void set_bitmap_uptodate(struct buffer_head *bh) extern wait_queue_head_t ext4__ioend_wq[EXT4_WQ_HASH_SZ]; extern struct mutex ext4__aio_mutex[EXT4_WQ_HASH_SZ]; +#define EXT4_RESIZING 0 +extern int ext4_resize_begin(struct super_block *sb); +extern void ext4_resize_end(struct super_block *sb); + #endif /* __KERNEL__ */ #endif /* _EXT4_H */ diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c index 808c554..f18bfe3 100644 --- a/fs/ext4/ioctl.c +++ b/fs/ext4/ioctl.c @@ -202,8 +202,9 @@ setversion_out: struct super_block *sb = inode->i_sb; int err, err2=0; - if (!capable(CAP_SYS_RESOURCE)) - return -EPERM; + err = ext4_resize_begin(sb); + if (err) + return err; if (get_user(n_blocks_count, (__u32 __user *)arg)) return -EFAULT; @@ -221,6 +222,7 @@ setversion_out: if (err == 0) err = err2; mnt_drop_write(filp->f_path.mnt); + ext4_resize_end(sb); return err; } @@ -271,8 +273,9 @@ mext_out: struct super_block *sb = inode->i_sb; int err, err2=0; - if (!capable(CAP_SYS_RESOURCE)) - return -EPERM; + err = ext4_resize_begin(sb); + if (err) + return err; if (copy_from_user(&input, (struct ext4_new_group_input __user *)arg, sizeof(input))) @@ -291,6 +294,7 @@ mext_out: if (err == 0) err = err2; mnt_drop_write(filp->f_path.mnt); + ext4_resize_end(sb); return err; } diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c index 80bbc9c..0213f63 100644 --- a/fs/ext4/resize.c +++ b/fs/ext4/resize.c @@ -16,6 +16,25 @@ #include "ext4_jbd2.h" +int ext4_resize_begin(struct super_block *sb) +{ + int ret = 0; + + if (!capable(CAP_SYS_RESOURCE)) + return -EPERM; + + if (test_and_set_bit_lock(EXT4_RESIZING, &EXT4_SB(sb)->s_resize_flags)) + ret = -EBUSY; + + return ret; +} + +void ext4_resize_end(struct super_block *sb) +{ + clear_bit_unlock(EXT4_RESIZING, &EXT4_SB(sb)->s_resize_flags); + smp_mb__after_clear_bit(); +} + #define outside(b, first, last) ((b) < (first) || (b) >= (last)) #define inside(b, first, last) ((b) >= (first) && (b) < (last)) @@ -181,11 +200,7 @@ static int setup_new_group_blocks(struct super_block *sb, if (IS_ERR(handle)) return PTR_ERR(handle); - mutex_lock(&sbi->s_resize_lock); - if (input->group != sbi->s_groups_count) { - err = -EBUSY; - goto exit_journal; - } + BUG_ON(input->group != sbi->s_groups_count); if (IS_ERR(bh = bclean(handle, sb, input->block_bitmap))) { err = PTR_ERR(bh); @@ -285,7 +300,6 @@ exit_bh: brelse(bh); exit_journal: - mutex_unlock(&sbi->s_resize_lock); if ((err2 = ext4_journal_stop(handle)) && !err) err = err2; @@ -799,13 +813,6 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input) goto exit_put; } - mutex_lock(&sbi->s_resize_lock); - if (input->group != sbi->s_groups_count) { - ext4_warning(sb, "multiple resizers run on filesystem!"); - err = -EBUSY; - goto exit_journal; - } - if ((err = ext4_journal_get_write_access(handle, sbi->s_sbh))) goto exit_journal; @@ -829,7 +836,6 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input) /* * OK, now we've set up the new group. Time to make it active. * - * We do not lock all allocations via s_resize_lock * so we have to be safe wrt. concurrent accesses the group * data. So we need to be careful to set all of the relevant * group descriptor data etc. *before* we enable the group. @@ -886,13 +892,9 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input) * * The precise rules we use are: * - * * Writers of s_groups_count *must* hold s_resize_lock - * AND * * Writers must perform a smp_wmb() after updating all dependent * data and before modifying the groups count * - * * Readers must hold s_resize_lock over the access - * OR * * Readers must perform an smp_rmb() after reading the groups count * and before reading any dependent data. * @@ -937,7 +939,6 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input) ext4_handle_dirty_super(handle, sb); exit_journal: - mutex_unlock(&sbi->s_resize_lock); if ((err2 = ext4_journal_stop(handle)) && !err) err = err2; if (!err) { @@ -972,9 +973,6 @@ int ext4_group_extend(struct super_block *sb, struct ext4_super_block *es, int err; ext4_group_t group; - /* We don't need to worry about locking wrt other resizers just - * yet: we're going to revalidate es->s_blocks_count after - * taking the s_resize_lock below. */ o_blocks_count = ext4_blocks_count(es); if (test_opt(sb, DEBUG)) @@ -995,7 +993,7 @@ int ext4_group_extend(struct super_block *sb, struct ext4_super_block *es, if (n_blocks_count < o_blocks_count) { ext4_warning(sb, "can't shrink FS - resize aborted"); - return -EBUSY; + return -EINVAL; } /* Handle the remaining blocks in the last group only. */ @@ -1038,24 +1036,13 @@ int ext4_group_extend(struct super_block *sb, struct ext4_super_block *es, goto exit_put; } - mutex_lock(&EXT4_SB(sb)->s_resize_lock); - if (o_blocks_count != ext4_blocks_count(es)) { - ext4_warning(sb, "multiple resizers run on filesystem!"); - mutex_unlock(&EXT4_SB(sb)->s_resize_lock); - ext4_journal_stop(handle); - err = -EBUSY; - goto exit_put; - } - if ((err = ext4_journal_get_write_access(handle, EXT4_SB(sb)->s_sbh))) { ext4_warning(sb, "error %d on journal write access", err); - mutex_unlock(&EXT4_SB(sb)->s_resize_lock); ext4_journal_stop(handle); goto exit_put; } ext4_blocks_count_set(es, o_blocks_count + add); - mutex_unlock(&EXT4_SB(sb)->s_resize_lock); ext4_debug("freeing blocks %llu through %llu\n", o_blocks_count, o_blocks_count + add); /* We add the blocks to the bitmap and set the group need init bit */ diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 143d763..cfe9f39 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -3500,7 +3500,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent) INIT_LIST_HEAD(&sbi->s_orphan); /* unlinked but open files */ mutex_init(&sbi->s_orphan_lock); - mutex_init(&sbi->s_resize_lock); + sbi->s_resize_flags = 0; sb->s_root = NULL; -- 2.7.4