From: Christoph Hellwig <hch@lst.de>
To: David Howells <dhowells@redhat.com>
Cc: mbobrowski@mbobrowski.org, darrick.wong@oracle.com, jack@suse.cz,
hch@lst.de, linux-ext4@vger.kernel.org,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: Is ext4_dio_read_iter() broken? - and xfs_file_dio_aio_read()
Date: Thu, 12 Mar 2020 11:42:39 +0100 [thread overview]
Message-ID: <20200312104239.GA13235@lst.de> (raw)
In-Reply-To: <1015227.1584007677@warthog.procyon.org.uk>
On Thu, Mar 12, 2020 at 10:07:57AM +0000, David Howells wrote:
> David Howells <dhowells@redhat.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?
The iocb is refcounted and only completed when the refcount hits zero,
and an extra reference is held until the submission has completed.
Take a look at iocb_put().
> 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.
the file reference also hold an inode reference.
>
> 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.
In addition to that DAX never executes asynchronously.
> And xfs_file_dio_aio_read() appears to be broken as it touches the inode after
> calling iomap_dio_rw() to unlock it.
Same as above.
next prev parent reply other threads:[~2020-03-12 10:42 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-12 9:19 Is ext4_dio_read_iter() broken? David Howells
2020-03-12 10:07 ` Is ext4_dio_read_iter() broken? - and xfs_file_dio_aio_read() David Howells
2020-03-12 10:42 ` Christoph Hellwig [this message]
2020-03-12 10:49 ` David Howells
2020-03-12 10:53 ` Christoph Hellwig
2020-03-12 10:20 ` Is ext4_dio_read_iter() broken? Matthew Bobrowski
2020-03-12 10:26 ` btrfs may be broken too - " David Howells
2020-03-12 23:23 ` Dave Chinner
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