Re: [PATCH RFC] ashmem: Fix lockdep RECLAIM_FS false positive

[NeilBrown]

On Wed, Feb 07 2018, Joel Fernandes wrote:

> Hi Peter,
>
> On Wed, Feb 7, 2018 at 8:58 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> [...]
>>
>>> Lockdep reports this issue when GFP_FS is infact set, and we enter
>>> this path and acquire the lock. So lockdep seems to be doing the right
>>> thing however by design it is reporting a false-positive.
>>
>> So I'm not seeing how its a false positive. fs/inode.c sets a different
>> lock class per filesystem type. So recursing on an i_mutex within a
>> filesystem does sound dodgy.
>
> But directory inodes and file inodes in the same filesystem share the
> same lock class right?

Not since v2.6.24
Commit: 14358e6ddaed ("lockdep: annotate dir vs file i_mutex")

You were using 4.9.60. so they should be separate....

Maybe shmem_get_inode() needs to call unlock_new_inode() or just
lockdep_annotate_inode_mutex_key() after inode_init_owner().

Maybe inode_init_owner() should call lockdep_annotate_inode_mutex_key()
directly.

NeilBrown

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