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Subject[PATCH] reiserfs writepage <-> preallocation race

This patch fixes a race when reiserfs_writepage tries to fill holes
in the file. The preallocation code relies on i_sem to protect
allocations for a given file, which won't work with concurrent
writepages (reiserfs doesn't lock_super during allocations).

The fix turns off preallocation when writepage is filling
holes, and removes the discard_prealloc calls from reiserfs_get_block.
That cleanup is done later when i_sem is actually held.

Alan, please apply.

-chris

--- linux-2.4.5/fs/reiserfs/inode.c Fri Jun 1 16:27:50 2001
+++ linux-2.4.5/fs/reiserfs/inode.c Wed Jun 6 14:59:01 2001
@@ -21,6 +21,7 @@
#define GET_BLOCK_CREATE 1 /* add anything you need to find block */
#define GET_BLOCK_NO_HOLE 2 /* return -ENOENT for file holes */
#define GET_BLOCK_READ_DIRECT 4 /* read the tail if indirect item not found */
+#define GET_BLOCK_NO_ISEM 8 /* i_sem is not held, don't preallocate */

//
// initially this function was derived from minix or ext2's analog and
@@ -489,6 +490,19 @@
return retval ;
}

+static inline int _allocate_block(struct reiserfs_transaction_handle *th,
+ struct inode *inode,
+ b_blocknr_t *allocated_block_nr,
+ unsigned long tag,
+ int flags) {
+
+#ifdef REISERFS_PREALLOCATE
+ if (!(flags & GET_BLOCK_NO_ISEM)) {
+ return reiserfs_new_unf_blocknrs2(th, inode, allocated_block_nr, tag);
+ }
+#endif
+ return reiserfs_new_unf_blocknrs (th, allocated_block_nr, tag);
+}
//
// initially this function was derived from ext2's analog and evolved
// as the prototype did. You'll need to look at the ext2 version to
@@ -581,11 +595,7 @@
goto research ;
}

-#ifdef REISERFS_PREALLOCATE
- repeat = reiserfs_new_unf_blocknrs2 (&th, inode, &allocated_block_nr, tag);
-#else
- repeat = reiserfs_new_unf_blocknrs (&th, &allocated_block_nr, tag);
-#endif
+ repeat = _allocate_block(&th, inode, &allocated_block_nr, tag, create);

if (repeat == NO_DISK_SPACE) {
/* restart the transaction to give the journal a chance to free
@@ -593,11 +603,7 @@
** research if we succeed on the second try
*/
restart_transaction(&th, inode, &path) ;
-#ifdef REISERFS_PREALLOCATE
- repeat = reiserfs_new_unf_blocknrs2 (&th, inode, &allocated_block_nr, tag);
-#else
- repeat = reiserfs_new_unf_blocknrs (&th, &allocated_block_nr, tag);
-#endif
+ repeat = _allocate_block(&th, inode,&allocated_block_nr,tag,create);

if (repeat != NO_DISK_SPACE) {
goto research ;
@@ -684,10 +690,6 @@
retval = reiserfs_insert_item (&th, &path, &tmp_key, &tmp_ih, (char *)&unp);
if (retval) {
reiserfs_free_block (&th, allocated_block_nr);
-
-#ifdef REISERFS_PREALLOCATE
- reiserfs_discard_prealloc (&th, inode);
-#endif
goto failure; // retval == -ENOSPC or -EIO or -EEXIST
}
if (unp)
@@ -735,10 +737,6 @@
mark_buffer_uptodate (unbh, 1);
if (retval) {
reiserfs_free_block (&th, allocated_block_nr);
-
-#ifdef REISERFS_PREALLOCATE
- reiserfs_discard_prealloc (&th, inode);
-#endif
goto failure;
}
/* we've converted the tail, so we must
@@ -784,10 +782,6 @@
retval = reiserfs_paste_into_item (&th, &path, &tmp_key, (char *)&un, UNFM_P_SIZE);
if (retval) {
reiserfs_free_block (&th, allocated_block_nr);
-
-#ifdef REISERFS_PREALLOCATE
- reiserfs_discard_prealloc (&th, inode);
-#endif
goto failure;
}
if (un.unfm_nodenum)
@@ -824,6 +818,8 @@
reiserfs_warning ("vs-: reiserfs_get_block: "
"%k should not be found", &key);
retval = -EEXIST;
+ if (allocated_block_nr)
+ reiserfs_free_block (&th, allocated_block_nr);
pathrelse(&path) ;
goto failure;
}
@@ -872,6 +868,8 @@
inode->i_generation = INODE_PKEY (inode)->k_dir_id;
inode->i_blksize = PAGE_SIZE;

+ INIT_LIST_HEAD(&inode->u.reiserfs_i.i_prealloc_list) ;
+
if (stat_data_v1 (ih)) {
struct stat_data_v1 * sd = (struct stat_data_v1 *)B_I_PITEM (bh, ih);
unsigned long blocks;
@@ -1427,6 +1425,8 @@
inode->u.reiserfs_i.i_first_direct_byte = S_ISLNK(mode) ? 1 :
U32_MAX/*NO_BYTES_IN_DIRECT_ITEM*/;

+ INIT_LIST_HEAD(&inode->u.reiserfs_i.i_prealloc_list) ;
+
if (old_format_only (sb))
inode2sd_v1 (&sd, inode);
else
@@ -1725,7 +1725,8 @@
/* this is where we fill in holes in the file. */
if (use_get_block) {
kmap(bh_result->b_page) ;
- retval = reiserfs_get_block(inode, block, bh_result, 1) ;
+ retval = reiserfs_get_block(inode, block, bh_result,
+ GET_BLOCK_CREATE | GET_BLOCK_NO_ISEM) ;
kunmap(bh_result->b_page) ;
if (!retval) {
if (!buffer_mapped(bh_result) || bh_result->b_blocknr == 0) {
-
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