Re: [PATCH] ext4: fix deadlock of i_data_sem in ext4_mark_inode_dirty()

Li Xi
2014-09-05T04:44:50Z

On Fri, Sep 5, 2014 at 11:30 AM, Theodore Ts'o <tytso@mit.edu> wrote:
> On Fri, Sep 05, 2014 at 10:29:16AM +0800, Li Xi wrote:
>> On Fri, Sep 5, 2014 at 9:59 AM, Theodore Ts'o <tytso@mit.edu> wrote:
>> > On Thu, Sep 04, 2014 at 04:49:58PM +0800, Li Xi wrote:
>> >> There are multiple places where ext4_mark_inode_dirty() is called holding
>> >> write lock of EXT4_I(inode)->i_data_sem. However, if
>> >> ext4_mark_inode_dirty() needs to expand inode size, this will cause
>> >> deadlock when ext4_xattr_block_set() tries to get read lock of
>> >> EXT4_I(inode)->i_data_sem.
>> >
>> > This was with inline data enabled, right?
>> I hit this problem when starting a kernel with project quota support for ext4.
>> The ext4 file system was not formated with project quota feature so it tried
>> to extend the space for project ID. And this problem happened every time
>> when the kernel was rebooted. Inline data was not enable on that file
>> system. I am not sure whether this problem will happen under other
>> circumstances. :)
>
> I'm not understanding why expanding the inode size would result in
> needing to call ext4_xattr_block_set. Was that becuse you were
> storing the project quota in the xattr? I'm just trying to understand
> the context.
Yeah, you are right. The problem happened when the project ID was
saved as xattr. And I can't reproduce the same problem with the new
patches.
>
> Please also note that a recent set of patches (sent to the ext4 list
> and in the ext4 git tree) has removed the need for taking i_data_sem
> in xattr.c:
>
> http://patchwork.ozlabs.org/patch/385347
> http://patchwork.ozlabs.org/patch/385348
> http://patchwork.ozlabs.org/patch/385346
>
> (It's the 2/3 patch that removes taking i_data_sem read lock in xattr.c.)
>
Great! Please ignore this patch since it won't be a problem
any more.

Regards,

- Li Xi