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authorJan Kara <jack@suse.cz>2022-07-12 13:54:27 +0300
committerTheodore Ts'o <tytso@mit.edu>2022-08-03 06:56:25 +0300
commit1189d8ec5105f7628fb0e3a6988cbf0d0cbfedeb (patch)
treef7365028252193ab01236fa973e133f4313f24eb /fs/ext2
parentb67798d55185ba4471f70b67b3f7c2866f216499 (diff)
downloadlinux-1189d8ec5105f7628fb0e3a6988cbf0d0cbfedeb.tar.xz
ext2: avoid deleting xattr block that is being reused
Currently when we decide to reuse xattr block we detect the case when the last reference to xattr block is being dropped at the same time and cancel the reuse attempt. Convert ext2 to a new scheme when as soon as matching mbcache entry is found, we wait with dropping the last xattr block reference until mbcache entry reference is dropped (meaning either the xattr block reference is increased or we decided not to reuse the block). Signed-off-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20220712105436.32204-8-jack@suse.cz Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Diffstat (limited to 'fs/ext2')
-rw-r--r--fs/ext2/xattr.c58
1 files changed, 29 insertions, 29 deletions
diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
index 37ce495eb279..641abfa4b718 100644
--- a/fs/ext2/xattr.c
+++ b/fs/ext2/xattr.c
@@ -522,17 +522,18 @@ bad_block:
lock_buffer(bh);
if (header->h_refcount == cpu_to_le32(1)) {
__u32 hash = le32_to_cpu(header->h_hash);
+ struct mb_cache_entry *oe;
- ea_bdebug(bh, "modifying in-place");
+ oe = mb_cache_entry_delete_or_get(EA_BLOCK_CACHE(inode),
+ hash, bh->b_blocknr);
+ if (!oe) {
+ ea_bdebug(bh, "modifying in-place");
+ goto update_block;
+ }
/*
- * This must happen under buffer lock for
- * ext2_xattr_set2() to reliably detect modified block
+ * Someone is trying to reuse the block, leave it alone
*/
- mb_cache_entry_delete(EA_BLOCK_CACHE(inode), hash,
- bh->b_blocknr);
-
- /* keep the buffer locked while modifying it. */
- goto update_block;
+ mb_cache_entry_put(EA_BLOCK_CACHE(inode), oe);
}
unlock_buffer(bh);
ea_bdebug(bh, "cloning");
@@ -656,16 +657,29 @@ static void ext2_xattr_release_block(struct inode *inode,
{
struct mb_cache *ea_block_cache = EA_BLOCK_CACHE(inode);
+retry_ref:
lock_buffer(bh);
if (HDR(bh)->h_refcount == cpu_to_le32(1)) {
__u32 hash = le32_to_cpu(HDR(bh)->h_hash);
+ struct mb_cache_entry *oe;
/*
- * This must happen under buffer lock for
- * ext2_xattr_set2() to reliably detect freed block
+ * This must happen under buffer lock to properly
+ * serialize with ext2_xattr_set() reusing the block.
*/
- mb_cache_entry_delete(ea_block_cache, hash,
- bh->b_blocknr);
+ oe = mb_cache_entry_delete_or_get(ea_block_cache, hash,
+ bh->b_blocknr);
+ if (oe) {
+ /*
+ * Someone is trying to reuse the block. Wait
+ * and retry.
+ */
+ unlock_buffer(bh);
+ mb_cache_entry_wait_unused(oe);
+ mb_cache_entry_put(ea_block_cache, oe);
+ goto retry_ref;
+ }
+
/* Free the old block. */
ea_bdebug(bh, "freeing");
ext2_free_blocks(inode, bh->b_blocknr, 1);
@@ -929,7 +943,7 @@ ext2_xattr_cache_find(struct inode *inode, struct ext2_xattr_header *header)
if (!header->h_hash)
return NULL; /* never share */
ea_idebug(inode, "looking for cached blocks [%x]", (int)hash);
-again:
+
ce = mb_cache_entry_find_first(ea_block_cache, hash);
while (ce) {
struct buffer_head *bh;
@@ -941,22 +955,8 @@ again:
inode->i_ino, (unsigned long) ce->e_value);
} else {
lock_buffer(bh);
- /*
- * We have to be careful about races with freeing or
- * rehashing of xattr block. Once we hold buffer lock
- * xattr block's state is stable so we can check
- * whether the block got freed / rehashed or not.
- * Since we unhash mbcache entry under buffer lock when
- * freeing / rehashing xattr block, checking whether
- * entry is still hashed is reliable.
- */
- if (hlist_bl_unhashed(&ce->e_hash_list)) {
- mb_cache_entry_put(ea_block_cache, ce);
- unlock_buffer(bh);
- brelse(bh);
- goto again;
- } else if (le32_to_cpu(HDR(bh)->h_refcount) >
- EXT2_XATTR_REFCOUNT_MAX) {
+ if (le32_to_cpu(HDR(bh)->h_refcount) >
+ EXT2_XATTR_REFCOUNT_MAX) {
ea_idebug(inode, "block %ld refcount %d>%d",
(unsigned long) ce->e_value,
le32_to_cpu(HDR(bh)->h_refcount),