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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 <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Yongqiang Yang 2011-07-26 21:35:44 -04:00 committed by Theodore Ts'o
parent 2d859db3e4
commit 8f82f840ec
4 changed files with 36 additions and 40 deletions
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7
fs/ext4/ext4.h
View File

@ -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 */

12
fs/ext4/ioctl.c
View File

@ -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;
}

55
fs/ext4/resize.c
View File

@ -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 */

2
fs/ext4/super.c
View File

@ -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;