On 2023/8/14 20:46, Jan Kara wrote:
On Fri 11-08-23 11:38:56, Ye Bin wrote:
There's a issue as follows:
Block Allocation Reservation Windows Map (ext2_try_to_allocate_with_rsv):
reservation window 0x000000006f105382 start: 0, end: 0
reservation window 0x000000008fd1a555 start: 1044, end: 1059
Window map complete.
kernel BUG at fs/ext2/balloc.c:1158!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
RIP: 0010:ext2_try_to_allocate_with_rsv.isra.0+0x15c4/0x1800
Call Trace:
<TASK>
ext2_new_blocks+0x935/0x1690
ext2_new_block+0x73/0xa0
ext2_xattr_set2+0x74f/0x1730
ext2_xattr_set+0x12b6/0x2260
ext2_xattr_user_set+0x9c/0x110
__vfs_setxattr+0x139/0x1d0
__vfs_setxattr_noperm+0xfc/0x370
__vfs_setxattr_locked+0x205/0x2c0
vfs_setxattr+0x19d/0x3b0
do_setxattr+0xff/0x220
setxattr+0x123/0x150
path_setxattr+0x193/0x1e0
__x64_sys_setxattr+0xc8/0x170
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
Above issue may happens as follows:
setxattr write back
ext2_xattr_set
ext2_xattr_set2
ext2_new_block
ext2_new_blocks
ext2_try_to_allocate_with_rsv
alloc_new_reservation
--> group=0 [0, 1023] rsv [1016, 1023]
do_writepages
mpage_writepages
write_cache_pages
__mpage_writepage
ext2_get_block
ext2_get_blocks
ext2_alloc_branch
ext2_new_blocks
ext2_try_to_allocate_with_rsv
alloc_new_reservation
-->group=1 [1024, 2047] rsv [1044, 1059]
if ((my_rsv->rsv_start > group_last_block) ||
(my_rsv->rsv_end < group_first_block)
rsv_window_dump
BUG();
Now ext2 mkwrite delay allocate new blocks. So there maybe allocate blocks when
do write back. However, there is no concurrent protection between
ext2_xattr_set() and do_writepages().
To solve about issue hold '&ei->truncate_mutex' lock when new block for xattr.
Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
Thanks for the patch! I agree the handling of reservation window and its
use for block allocation needs to be protected by ei->i_truncate_mutex.
However in this particular case of xattr allocation where we want to
allocate just one block which is completely independent of file data, I'd
rather choose to make ext2_new_blocks() ignore the reservation window (set
my_rsv to NULL). There's already a logic at the beginning of
ext2_new_blocks() deciding whether to use the reservation window or not and
we could extend it - probably by adding flags argument to it a introducing
a NORESERVE flag.
Also as a preparatory patch, I'd just remove ext2_new_block() and opencode
it in the xattr code since it has only that one user anyway.
Honza
Thanks for your suggestion. I will send new version according to your
suggestion.
---
fs/ext2/balloc.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
index c8049c90323d..039f655febfd 100644
--- a/fs/ext2/balloc.c
+++ b/fs/ext2/balloc.c
@@ -1432,8 +1432,14 @@ ext2_fsblk_t ext2_new_blocks(struct inode *inode, ext2_fsblk_t goal,
ext2_fsblk_t ext2_new_block(struct inode *inode, unsigned long goal, int *errp)
{
unsigned long count = 1;
+ struct ext2_inode_info *ei = EXT2_I(inode);
+ ext2_fsblk_t ret;
+
+ mutex_lock(&ei->truncate_mutex);
+ ret = ext2_new_blocks(inode, goal, &count, errp);
+ mutex_unlock(&ei->truncate_mutex);
- return ext2_new_blocks(inode, goal, &count, errp);
+ return ret;
}
#ifdef EXT2FS_DEBUG
--
2.31.1
