> On Thu, Aug 24, 2023 at 03:43:52PM +0800, cheng.lin130@xxxxxxxxxx wrote:
>> From: Cheng Lin <cheng.lin130@xxxxxxxxxx>
>> An dir nlinks overflow which down form 0 to 0xffffffff, cause the
>> directory to become unusable until the next xfs_repair run.
>>
>> Introduce protection for drop nlink to reduce the impact of this.
>> And produce a warning for directory nlink error during remove.
>>
>> Signed-off-by: Cheng Lin <cheng.lin130@xxxxxxxxxx>
>> ---
>> fs/xfs/xfs_inode.c | 16 +++++++++++++++-
>> 1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
>> index 9e62cc5..536dbe4 100644
>> --- a/fs/xfs/xfs_inode.c
>> +++ b/fs/xfs/xfs_inode.c
>> @@ -919,6 +919,15 @@ STATIC int xfs_iunlink_remove(struct xfs_trans *tp, struct xfs_perag *pag,
>> xfs_trans_t *tp,
>> xfs_inode_t *ip)
>> {
>> + xfs_mount_t *mp;
>> +
>> + if (VFS_I(ip)->i_nlink == 0) {
>> + mp = ip->i_mount;
>> + xfs_warn(mp, "%s: Deleting inode %llu with no links.",
>> + __func__, ip->i_ino);
>> + return 0;
>> + }
>> +
>> xfs_trans_ichgtime(tp, ip, XFS_ICHGTIME_CHG);
>>
>> drop_nlink(VFS_I(ip));
> I'm not sure how nlink would ever get to 0xFFFFFFFF since the VFS won't
> let a link count exceed s_max_links, and XFS sets that to 0x7FFFFFFF.
> Unless, of course, you did that outside of Linux.
In VFS drop_nlink() only produce a warning, when (inode->i_nlink == 0),
not prevent its self-reduce(inode->__i_nlink--), cause it underflow
from 0 to 0xffffffff. In the old kernel version, this situation was
encountered, but I don't know how it happened. It was already a scene
with directory errors: "Too many links".
kernel: WARNING: CPU: 12 PID: 12928 at fs/inode.c:286 drop_nlink+0x3e/0x50
kernel: CPU: 12 PID: 12928 Comm: gbased Tainted: G W OE ------------ T 3.10.0-693.21.1.el7.x86_64 #1
kernel: Hardware name: HPE ProLiant BL460c Gen10/ProLiant BL460c Gen10, BIOS I41 01/23/2021
kernel: Call Trace:-------------------
kernel: [<ffffffff816c5fce>] dump_stack+0x19/0x1b
kernel: [<ffffffff8108dfa8>] __warn+0xd8/0x100/*
kernel: [<ffffffff8108e0ed>] warn_slowpath_null+0x1d/0x20
kernel: [<ffffffff8122cdfe>] drop_nlink+0x3e/0x50
kernel: [<ffffffffc03cdc78>] xfs_droplink+0x28/0x60 [xfs]
kernel: [<ffffffffc03cf87a>] xfs_remove+0x2aa/0x320 [xfs]
kernel: [<ffffffffc03c9f7a>] xfs_vn_unlink+0x5a/0xa0 [xfs]
kernel: [<ffffffff8121f19c>] vfs_rmdir+0xdc/0x150
kernel: [<ffffffff81221e41>] do_rmdir+0x1f1/0x220
kernel: [<ffffffff81223046>] SyS_rmdir+0x16/0x20
kernel: [<ffffffff816d86d5>] system_call_fastpath+0x1c/0x21
> That said, why wouldn't you /pin/ the link count at -1U instead of
> allowing it to overflow to zero?
> Could you please take a look at this patch that's waiting in my
> submission queue?
> https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?h=inode-repair-improvements&id=05f5a82efa6395c92038e18e008aaf7154238f27
I think the XFS_NLINK_PINNEED(~0U) can be used prevent Overflow in inc_nlink().
Is it better to compare i_nlink with (0U) in drop_nlink() to prevent Underflow?
(like this patch does, do not make i_nlink underflow from 0 to 0xffffffff)
Thanks.
> --D
>> @@ -2442,7 +2451,12 @@ STATIC int xfs_iunlink_remove(struct xfs_trans *tp, struct xfs_perag *pag,
>> */
>> if (is_dir) {
>> ASSERT(VFS_I(ip)->i_nlink >= 2);
>> - if (VFS_I(ip)->i_nlink != 2) {
>> + if (VFS_I(ip)->i_nlink < 2) {
>> + xfs_warn(ip->i_mount,
>> + "%s: Remove dir (inode %llu) with invalid links.",
>> + __func__, ip->i_ino);
>> + }
>> + if (VFS_I(ip)->i_nlink > 2) {
>> error = -ENOTEMPTY;
>> goto out_trans_cancel;
>> }
>> --
>> 1.8.3.1
