@@ -82,9 +82,6 @@ static inline sysv_zone_t *block_end(struct buffer_head *bh)
return (sysv_zone_t*)((char*)bh->b_data + bh->b_size);
}
-/*
- * Requires read_lock(&pointers_lock) or write_lock(&pointers_lock)
- */
static Indirect *get_branch(struct inode *inode,
int depth,
int offsets[],
@@ -104,15 +101,18 @@ static Indirect *get_branch(struct inode *inode,
bh = sb_bread(sb, block);
if (!bh)
goto failure;
+ read_lock(&pointers_lock);
if (!verify_chain(chain, p))
goto changed;
add_chain(++p, bh, (sysv_zone_t*)bh->b_data + *++offsets);
+ read_unlock(&pointers_lock);
if (!p->key)
goto no_block;
}
return NULL;
changed:
+ read_unlock(&pointers_lock);
brelse(bh);
*err = -EAGAIN;
goto no_block;
@@ -214,9 +214,7 @@ static int get_block(struct inode *inode, sector_t iblock, struct buffer_head *b
goto out;
reread:
- read_lock(&pointers_lock);
partial = get_branch(inode, depth, offsets, chain, &err);
- read_unlock(&pointers_lock);
/* Simplest case - block found, no allocation needed */
if (!partial) {
@@ -286,9 +284,9 @@ static Indirect *find_shared(struct inode *inode,
*top = 0;
for (k = depth; k > 1 && !offsets[k-1]; k--)
;
+ partial = get_branch(inode, k, offsets, chain, &err);
write_lock(&pointers_lock);
- partial = get_branch(inode, k, offsets, chain, &err);
if (!partial)
partial = chain + k-1;
/*
syzbot is reporting sleep in atomic context in SysV filesystem [1], for sb_bread() is called with rw_spinlock held. A "write_lock(&pointers_lock) => read_lock(&pointers_lock) deadlock" bug and a "sb_bread() with write_lock(&pointers_lock)" bug were introduced by "Replace BKL for chain locking with sysvfs-private rwlock" in Linux 2.5.12. Then, "[PATCH] err1-40: sysvfs locking fix" in Linux 2.6.8 fixed the former bug by moving pointers_lock lock to the callers, but instead introduced a "sb_bread() with read_lock(&pointers_lock)" bug (which made this problem easier to hit). Al Viro suggested that why not to do like get_branch()/get_block()/ find_shared() in Minix filesystem does. And doing like that is a revert of "[PATCH] err1-40: sysvfs locking fix" except that get_branch() from find_shared() is called without write_lock(&pointers_lock). Reported-by: syzbot <syzbot+69b40dc5fd40f32c199f@syzkaller.appspotmail.com> Link: https://syzkaller.appspot.com/bug?extid=69b40dc5fd40f32c199f Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> --- Changes in v2: Correct patch description. fs/sysv/itree.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-)