ufs: don't use lock_ufs() for block pointers tree protection
* stores to block pointers are under per-inode seqlock (meta_lock) and
mutex (truncate_mutex)
* fetches of block pointers are either under truncate_mutex, or wrapped
into seqretry loop on meta_lock
* all changes of ->i_size are under truncate_mutex and i_mutex
* all changes of ->i_lastfrag are under truncate_mutex
It's similar to what ext2 is doing; the main difference is that unlike
ext2 we can't rely upon the atomicity of stores into block pointers -
on UFS2 they are 64bit. So we can't cut the corner when switching
a pointer from NULL to non-NULL as we could in ext2_splice_branch()
and need to use meta_lock on all modifications.
We use seqlock where ext2 uses rwlock; ext2 could probably also benefit
from such change...
Another non-trivial difference is that with UFS we *cannot* have reader
grab truncate_mutex in case of race - it has to keep retrying. That
might be possible to change, but not until we lift tail unpacking
several levels up in call chain.
After that commit we do *NOT* hold fs-wide serialization on accesses
to block pointers anymore. Moreover, lock_ufs() can become a normal
mutex now - it's only used on statfs, remount and sync_fs and none
of those uses are recursive. As the matter of fact, *now* it can be
collapsed with ->s_lock, and be eventually replaced with saner
per-cylinder-group spinlocks, but that's a separate story.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ufs/inode.c b/fs/ufs/inode.c
index a4fc3ad..100f93c 100644
--- a/fs/ufs/inode.c
+++ b/fs/ufs/inode.c
@@ -41,8 +41,6 @@
#include "swab.h"
#include "util.h"
-static u64 ufs_frag_map(struct inode *inode, sector_t frag, bool needs_lock);
-
static int ufs_block_to_path(struct inode *inode, sector_t i_block, sector_t offsets[4])
{
struct ufs_sb_private_info *uspi = UFS_SB(inode->i_sb)->s_uspi;
@@ -75,12 +73,53 @@
return n;
}
+typedef struct {
+ void *p;
+ union {
+ __fs32 key32;
+ __fs64 key64;
+ };
+ struct buffer_head *bh;
+} Indirect;
+
+static inline int grow_chain32(struct ufs_inode_info *ufsi,
+ struct buffer_head *bh, __fs32 *v,
+ Indirect *from, Indirect *to)
+{
+ Indirect *p;
+ unsigned seq;
+ to->bh = bh;
+ do {
+ seq = read_seqbegin(&ufsi->meta_lock);
+ to->key32 = *(__fs32 *)(to->p = v);
+ for (p = from; p <= to && p->key32 == *(__fs32 *)p->p; p++)
+ ;
+ } while (read_seqretry(&ufsi->meta_lock, seq));
+ return (p > to);
+}
+
+static inline int grow_chain64(struct ufs_inode_info *ufsi,
+ struct buffer_head *bh, __fs64 *v,
+ Indirect *from, Indirect *to)
+{
+ Indirect *p;
+ unsigned seq;
+ to->bh = bh;
+ do {
+ seq = read_seqbegin(&ufsi->meta_lock);
+ to->key64 = *(__fs64 *)(to->p = v);
+ for (p = from; p <= to && p->key64 == *(__fs64 *)p->p; p++)
+ ;
+ } while (read_seqretry(&ufsi->meta_lock, seq));
+ return (p > to);
+}
+
/*
* Returns the location of the fragment from
* the beginning of the filesystem.
*/
-static u64 ufs_frag_map(struct inode *inode, sector_t frag, bool needs_lock)
+static u64 ufs_frag_map(struct inode *inode, sector_t frag)
{
struct ufs_inode_info *ufsi = UFS_I(inode);
struct super_block *sb = inode->i_sb;
@@ -88,12 +127,10 @@
u64 mask = (u64) uspi->s_apbmask>>uspi->s_fpbshift;
int shift = uspi->s_apbshift-uspi->s_fpbshift;
sector_t offsets[4], *p;
+ Indirect chain[4], *q = chain;
int depth = ufs_block_to_path(inode, frag >> uspi->s_fpbshift, offsets);
- u64 ret = 0L;
- __fs32 block;
- __fs64 u2_block = 0L;
unsigned flags = UFS_SB(sb)->s_flags;
- u64 temp = 0L;
+ u64 res = 0;
UFSD(": frag = %llu depth = %d\n", (unsigned long long)frag, depth);
UFSD(": uspi->s_fpbshift = %d ,uspi->s_apbmask = %x, mask=%llx\n",
@@ -101,59 +138,73 @@
(unsigned long long)mask);
if (depth == 0)
- return 0;
+ goto no_block;
+again:
p = offsets;
- if (needs_lock)
- lock_ufs(sb);
if ((flags & UFS_TYPE_MASK) == UFS_TYPE_UFS2)
goto ufs2;
- block = ufsi->i_u1.i_data[*p++];
- if (!block)
- goto out;
+ if (!grow_chain32(ufsi, NULL, &ufsi->i_u1.i_data[*p++], chain, q))
+ goto changed;
+ if (!q->key32)
+ goto no_block;
while (--depth) {
+ __fs32 *ptr;
struct buffer_head *bh;
sector_t n = *p++;
- bh = sb_bread(sb, uspi->s_sbbase + fs32_to_cpu(sb, block)+(n>>shift));
+ bh = sb_bread(sb, uspi->s_sbbase +
+ fs32_to_cpu(sb, q->key32) + (n>>shift));
if (!bh)
- goto out;
- block = ((__fs32 *) bh->b_data)[n & mask];
- brelse (bh);
- if (!block)
- goto out;
+ goto no_block;
+ ptr = (__fs32 *)bh->b_data + (n & mask);
+ if (!grow_chain32(ufsi, bh, ptr, chain, ++q))
+ goto changed;
+ if (!q->key32)
+ goto no_block;
}
- ret = (u64) (uspi->s_sbbase + fs32_to_cpu(sb, block) + (frag & uspi->s_fpbmask));
- goto out;
+ res = fs32_to_cpu(sb, q->key32);
+ goto found;
+
ufs2:
- u2_block = ufsi->i_u1.u2_i_data[*p++];
- if (!u2_block)
- goto out;
-
+ if (!grow_chain64(ufsi, NULL, &ufsi->i_u1.u2_i_data[*p++], chain, q))
+ goto changed;
+ if (!q->key64)
+ goto no_block;
while (--depth) {
+ __fs64 *ptr;
struct buffer_head *bh;
sector_t n = *p++;
-
- temp = (u64)(uspi->s_sbbase) + fs64_to_cpu(sb, u2_block);
- bh = sb_bread(sb, temp +(u64) (n>>shift));
+ bh = sb_bread(sb, uspi->s_sbbase +
+ fs64_to_cpu(sb, q->key64) + (n>>shift));
if (!bh)
- goto out;
- u2_block = ((__fs64 *)bh->b_data)[n & mask];
- brelse(bh);
- if (!u2_block)
- goto out;
+ goto no_block;
+ ptr = (__fs64 *)bh->b_data + (n & mask);
+ if (!grow_chain64(ufsi, bh, ptr, chain, ++q))
+ goto changed;
+ if (!q->key64)
+ goto no_block;
}
- temp = (u64)uspi->s_sbbase + fs64_to_cpu(sb, u2_block);
- ret = temp + (u64) (frag & uspi->s_fpbmask);
+ res = fs64_to_cpu(sb, q->key64);
+found:
+ res += uspi->s_sbbase + (frag & uspi->s_fpbmask);
+no_block:
+ while (q > chain) {
+ brelse(q->bh);
+ q--;
+ }
+ return res;
-out:
- if (needs_lock)
- unlock_ufs(sb);
- return ret;
+changed:
+ while (q > chain) {
+ brelse(q->bh);
+ q--;
+ }
+ goto again;
}
/**
@@ -421,10 +472,9 @@
int ret, err, new;
unsigned long ptr,phys;
u64 phys64 = 0;
- bool needs_lock = (sbi->mutex_owner != current);
if (!create) {
- phys64 = ufs_frag_map(inode, fragment, needs_lock);
+ phys64 = ufs_frag_map(inode, fragment);
UFSD("phys64 = %llu\n", (unsigned long long)phys64);
if (phys64)
map_bh(bh_result, sb, phys64);
@@ -438,8 +488,7 @@
ret = 0;
bh = NULL;
- if (needs_lock)
- lock_ufs(sb);
+ mutex_lock(&UFS_I(inode)->truncate_mutex);
UFSD("ENTER, ino %lu, fragment %llu\n", inode->i_ino, (unsigned long long)fragment);
if (fragment >
@@ -501,8 +550,7 @@
set_buffer_new(bh_result);
map_bh(bh_result, sb, phys);
abort:
- if (needs_lock)
- unlock_ufs(sb);
+ mutex_unlock(&UFS_I(inode)->truncate_mutex);
return err;