Re: [RFC PATCH] nfs: avoid swap-over-NFS deadlock

[Jerome Marchand <jmarchan@redhat.com>]

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On 07/22/2015 02:23 PM, Trond Myklebust wrote:
> On Wed, Jul 22, 2015 at 4:10 AM, Jerome Marchand <jmarchan@redhat.com> wrote:
>>
>> Lockdep warns about a inconsistent {RECLAIM_FS-ON-W} ->
>> {IN-RECLAIM_FS-W} usage. The culpritt is the inode->i_mutex taken in
>> nfs_file_direct_write(). This code was introduced by commit a9ab5e840669
>> ("nfs: page cache invalidation for dio").
>> This naive test patch avoid to take the mutex on a swapfile and makes
>> lockdep happy again. However I don't know much about NFS code and I
>> assume it's probably not the proper solution. Any thought?
>>
>> Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
> 
> NFS is not the only O_DIRECT implementation to set the inode->i_mutex.
> Why can't this be fixed in the generic swap code instead of adding
> yet-another-exception-for-IS_SWAPFILE?

I meant to cc Mel. Just added him.

AFAIK NFS is the only filesystem that uses swap_activate. Other
swapfiles are handled more or less like block device (divided in a set
of contiguous ranges of disk block called swap extents), so there are
not affected by this possible deadlock.

Also nfs_direct_IO() is special in that it is called only from swap,
nfs_file_direct_write() however has other users.

Jerome
> 
> Cheers
>   Trond
> 



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