Re: [PATCH v2] xfs: fix mount hang during primary superblock recovery failure

[Long Li <leo.lilong@huawei.com>]

On Fri, Jan 10, 2025 at 09:40:16AM +0800, Long Li wrote:
> On Wed, Jan 08, 2025 at 08:41:42PM -0800, Darrick J. Wong wrote:
> > On Thu, Jan 09, 2025 at 10:13:20AM +0800, Long Li wrote:
> > > When mounting an image containing a log with sb modifications that require
> > > log replay, the mount process hang all the time and stack as follows:
> > > 
> > >   [root@localhost ~]# cat /proc/557/stack
> > >   [<0>] xfs_buftarg_wait+0x31/0x70
> > >   [<0>] xfs_buftarg_drain+0x54/0x350
> > >   [<0>] xfs_mountfs+0x66e/0xe80
> > >   [<0>] xfs_fs_fill_super+0x7f1/0xec0
> > >   [<0>] get_tree_bdev_flags+0x186/0x280
> > >   [<0>] get_tree_bdev+0x18/0x30
> > >   [<0>] xfs_fs_get_tree+0x1d/0x30
> > >   [<0>] vfs_get_tree+0x2d/0x110
> > >   [<0>] path_mount+0xb59/0xfc0
> > >   [<0>] do_mount+0x92/0xc0
> > >   [<0>] __x64_sys_mount+0xc2/0x160
> > >   [<0>] x64_sys_call+0x2de4/0x45c0
> > >   [<0>] do_syscall_64+0xa7/0x240
> > >   [<0>] entry_SYSCALL_64_after_hwframe+0x76/0x7e
> > > 
> > > During log recovery, while updating the in-memory superblock from the
> > > primary SB buffer, if an error is encountered, such as superblock
> > > corruption occurs or some other reasons, we will proceed to out_release
> > > and release the xfs_buf. However, this is insufficient because the
> > > xfs_buf's log item has already been initialized and the xfs_buf is held
> > > by the buffer log item as follows, the xfs_buf will not be released,
> > > causing the mount thread to hang.
> > 
> > Can you post a regression test for us, pretty please? :)
> > 
> 
> I performed regression testing by mounting specific images that can be
> obtained through fault injection on kernels without metadir feature support.
> I can provide it if anyone needs it.The image is big and inconvenient to send
> in the mail. The detailed steps are as follows:
> 
> 1) Kernel Build
>   - The latest realtime AG update bug [1] remains unfixed
>   - Build kernel without CONFIG_XFS_RT
>   
> 2) Mount XFS Image (superblock needs replay, incompatible with metadir and
>    no realtime subvolume)
> 
> 3) Mount Result Verification
>   - Without the current patch: mount thread hangs indefinitely
>   - With the current patch: mount thread does not hang, but XFS is shut down
> 
> The xfstests already have the fault injection test, and this test requires
> mounting specific images on specifically-compiled kernels, making it impractical
> to incorporate into xfstests.
> 

Sorry, forgot to add the fixed patch link:

[1] https://patchwork.kernel.org/project/xfs/patch/20241217042737.1755365-1-hch@lst.de/