From: Stephen Tweedie <sct@redhat.com>
There is a race in the existing reservations code: while we are allocating
from a reservation, another thread may be discarding the fd's existing
reservation as part of a separate allocation.
To avoid locking the reservation during the bitmap search for a free block, we
just take a temporary copy of the existing reservation during that search. To
minimise the cost, we use a seqlock to protect the per-filp reservation, using
a seqlock read when taking the temporary copy and locking for write only when
taking out a new reservation.
Fixes http://bugme.osdl.org/show_bug.cgi?id=3171
Signed-off-by: Stephen Tweedie <sct@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/fs/ext3/balloc.c | 35 ++++++++++++++++++++++++-----------
25-akpm/fs/ext3/ialloc.c | 3 ++-
25-akpm/fs/ext3/inode.c | 1 +
25-akpm/fs/ext3/super.c | 2 +-
25-akpm/include/linux/ext3_fs_i.h | 4 +++-
5 files changed, 31 insertions(+), 14 deletions(-)
diff -puN fs/ext3/balloc.c~ext3-reservations-smp-protect-the-reservation-during-allocation fs/ext3/balloc.c
--- 25/fs/ext3/balloc.c~ext3-reservations-smp-protect-the-reservation-during-allocation 2004-09-26 17:18:05.770781160 -0700
+++ 25-akpm/fs/ext3/balloc.c 2004-09-26 17:18:05.782779336 -0700
@@ -250,7 +250,7 @@ static void rsv_window_remove(struct sup
{
rsv->rsv_start = 0;
rsv->rsv_end = 0;
- rsv->rsv_alloc_hit = 0;
+ atomic_set(&rsv->rsv_alloc_hit, 0);
rb_erase(&rsv->rsv_node, &EXT3_SB(sb)->s_rsv_window_root);
}
@@ -856,7 +856,8 @@ static int alloc_new_reservation(struct
if (my_rsv->rsv_end + 1 > start_block)
start_block = my_rsv->rsv_end + 1;
search_head = my_rsv;
- if ((my_rsv->rsv_alloc_hit > (my_rsv->rsv_end - my_rsv->rsv_start + 1) / 2)) {
+ if ((atomic_read(&my_rsv->rsv_alloc_hit) >
+ (my_rsv->rsv_end - my_rsv->rsv_start + 1) / 2)) {
/*
* if we previously allocation hit ration is greater than half
* we double the size of reservation window next time
@@ -1035,27 +1036,39 @@ ext3_try_to_allocate_with_rsv(struct sup
* then we could go to allocate from the reservation window directly.
*/
while (1) {
- if (rsv_is_empty(&my_rsv->rsv_window) || (ret < 0) ||
- !goal_in_my_reservation(&my_rsv->rsv_window,
- goal, group, sb)) {
+ struct reserve_window rsv_copy;
+ unsigned int seq;
+
+ do {
+ seq = read_seqbegin(&my_rsv->rsv_seqlock);
+ rsv_copy._rsv_start = my_rsv->rsv_start;
+ rsv_copy._rsv_end = my_rsv->rsv_end;
+ } while (read_seqretry(&my_rsv->rsv_seqlock, seq));
+
+ if (rsv_is_empty(&rsv_copy) || (ret < 0) ||
+ !goal_in_my_reservation(&rsv_copy, goal, group, sb)) {
spin_lock(rsv_lock);
+ write_seqlock(&my_rsv->rsv_seqlock);
ret = alloc_new_reservation(my_rsv, goal, sb,
group, bitmap_bh);
+ rsv_copy._rsv_start = my_rsv->rsv_start;
+ rsv_copy._rsv_end = my_rsv->rsv_end;
+ write_sequnlock(&my_rsv->rsv_seqlock);
spin_unlock(rsv_lock);
if (ret < 0)
break; /* failed */
- if (!goal_in_my_reservation(&my_rsv->rsv_window,
- goal, group, sb))
+ if (!goal_in_my_reservation(&rsv_copy, goal, group, sb))
goal = -1;
}
- if ((my_rsv->rsv_start >= group_first_block + EXT3_BLOCKS_PER_GROUP(sb))
- || (my_rsv->rsv_end < group_first_block))
+ if ((rsv_copy._rsv_start >= group_first_block + EXT3_BLOCKS_PER_GROUP(sb))
+ || (rsv_copy._rsv_end < group_first_block))
BUG();
ret = ext3_try_to_allocate(sb, handle, group, bitmap_bh, goal,
- &my_rsv->rsv_window);
+ &rsv_copy);
if (ret >= 0) {
- my_rsv->rsv_alloc_hit++;
+ if (!read_seqretry(&my_rsv->rsv_seqlock, seq))
+ atomic_inc(&my_rsv->rsv_alloc_hit);
break; /* succeed */
}
}
diff -puN fs/ext3/ialloc.c~ext3-reservations-smp-protect-the-reservation-during-allocation fs/ext3/ialloc.c
--- 25/fs/ext3/ialloc.c~ext3-reservations-smp-protect-the-reservation-during-allocation 2004-09-26 17:18:05.771781008 -0700
+++ 25-akpm/fs/ext3/ialloc.c 2004-09-26 17:18:05.782779336 -0700
@@ -585,7 +585,8 @@ got:
ei->i_rsv_window.rsv_start = 0;
ei->i_rsv_window.rsv_end = 0;
atomic_set(&ei->i_rsv_window.rsv_goal_size, EXT3_DEFAULT_RESERVE_BLOCKS);
- ei->i_rsv_window.rsv_alloc_hit = 0;
+ atomic_set(&ei->i_rsv_window.rsv_alloc_hit, 0);
+ seqlock_init(&ei->i_rsv_window.rsv_seqlock);
ei->i_block_group = group;
ext3_set_inode_flags(inode);
diff -puN fs/ext3/inode.c~ext3-reservations-smp-protect-the-reservation-during-allocation fs/ext3/inode.c
--- 25/fs/ext3/inode.c~ext3-reservations-smp-protect-the-reservation-during-allocation 2004-09-26 17:18:05.773780704 -0700
+++ 25-akpm/fs/ext3/inode.c 2004-09-26 17:18:05.785778880 -0700
@@ -2461,6 +2461,7 @@ void ext3_read_inode(struct inode * inod
ei->i_rsv_window.rsv_start = 0;
ei->i_rsv_window.rsv_end= 0;
atomic_set(&ei->i_rsv_window.rsv_goal_size, EXT3_DEFAULT_RESERVE_BLOCKS);
+ seqlock_init(&ei->i_rsv_window.rsv_seqlock);
/*
* NOTE! The in-memory inode i_data array is in little-endian order
* even on big-endian machines: we do NOT byteswap the block numbers!
diff -puN fs/ext3/super.c~ext3-reservations-smp-protect-the-reservation-during-allocation fs/ext3/super.c
--- 25/fs/ext3/super.c~ext3-reservations-smp-protect-the-reservation-during-allocation 2004-09-26 17:18:05.776780248 -0700
+++ 25-akpm/fs/ext3/super.c 2004-09-26 17:18:05.787778576 -0700
@@ -1486,7 +1486,7 @@ static int ext3_fill_super (struct super
* _much_ simpler. */
sbi->s_rsv_window_head.rsv_start = 0;
sbi->s_rsv_window_head.rsv_end = 0;
- sbi->s_rsv_window_head.rsv_alloc_hit = 0;
+ atomic_set(&sbi->s_rsv_window_head.rsv_alloc_hit, 0);
atomic_set(&sbi->s_rsv_window_head.rsv_goal_size, 0);
rsv_window_add(sb, &sbi->s_rsv_window_head);
diff -puN include/linux/ext3_fs_i.h~ext3-reservations-smp-protect-the-reservation-during-allocation include/linux/ext3_fs_i.h
--- 25/include/linux/ext3_fs_i.h~ext3-reservations-smp-protect-the-reservation-during-allocation 2004-09-26 17:18:05.777780096 -0700
+++ 25-akpm/include/linux/ext3_fs_i.h 2004-09-26 17:18:05.788778424 -0700
@@ -18,6 +18,7 @@
#include <linux/rwsem.h>
#include <linux/rbtree.h>
+#include <linux/seqlock.h>
struct reserve_window {
__u32 _rsv_start; /* First byte reserved */
@@ -27,7 +28,8 @@ struct reserve_window {
struct reserve_window_node {
struct rb_node rsv_node;
atomic_t rsv_goal_size;
- __u32 rsv_alloc_hit;
+ atomic_t rsv_alloc_hit;
+ seqlock_t rsv_seqlock;
struct reserve_window rsv_window;
};
_