linux-ext4 - Re: Is ext4_dio_read_iter() broken?

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Date:   Thu, 12 Mar 2020 10:07:57 +0000
From:   David Howells <dhowells@...hat.com>
To:     mbobrowski@...browski.org, darrick.wong@...cle.com
Cc:     dhowells@...hat.com, jack@...e.cz, hch@....de,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: Is ext4_dio_read_iter() broken? - and xfs_file_dio_aio_read()

David Howells <dhowells@...hat.com> wrote:

> Is ext4_dio_read_iter() broken?  It calls:
> 
> 	file_accessed(iocb->ki_filp);
> 
> at the end of the function - but surely iocb should be expected to have been
> freed when iocb->ki_complete() was called?

I think it's actually worse than that.  You also can't call
inode_unlock_shared(inode) because you no longer own a ref on the inode since
->ki_complete() is expected to call fput() on iocb->ki_filp.

Yes, you own a shared lock on it, but unless somewhere along the
fput-dput-iput chain the inode lock is taken exclusively, the inode can be
freed whilst you're still holding the lock.

Oh - and ext4_dax_read_iter() is also similarly broken.

And xfs_file_dio_aio_read() appears to be broken as it touches the inode after
calling iomap_dio_rw() to unlock it.

David