linux-kernel - Re: [PATCH] aio: fix kernel bug when page is temporally busy

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Message-Id: <E29B98FF-8DDE-4AA5-AD65-75112B3E0DD6@oracle.com>
Date:	Thu, 15 Feb 2007 16:01:06 -0800
From:	Zach Brown <zach.brown@...cle.com>
To:	"Ananiev, Leonid I" <leonid.i.ananiev@...el.com>
Cc:	"Ken Chen" <kenchen@...gle.com>, <suparna@...ibm.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, "linux-aio" <linux-aio@...ck.org>,
	"Chris Mason" <chris.mason@...cle.com>
Subject: Re: [PATCH] aio: fix kernel bug when page is temporally busy


On Feb 15, 2007, at 3:32 PM, Ananiev, Leonid I wrote:

>>> If EIOCBRETRY then generic_file_aio_write() will be recalled for the
>>> same iocb.
>> Only if kick_iocb() is called.  It won't be called if i_i_p2_r() was
>> the only thing to return -EIOCBRETRY.
> It is not need to call kick_iocb()
> for generic_file_aio_write() calling.
> It is recalled without any wakeup waiting:
>         for (;;) {
>                 ret = filp->f_op->aio_write(&kiocb, &iov, 1,
> kiocb.ki_pos);
>                 if (ret != -EIOCBRETRY)
>                         break;
>                 wait_on_retry_sync_kiocb(&kiocb);
>         }
> Note: wait_on_retry_sync_kiocb() does not wait.

Yes it does.  It will not return until kiocbSetKicked() is called,  
and that is only called from kick_iocb().

>>> It overwrites -EIOCBQUEUED
> Do you mean that there is one more kernel bug which
> overwrites -EIOCBQUEUED by any errno or number of bytes and this
> new value is returned to caller as an IO result
> while IO is not finished yet.
>
> The proposed patch does not crate this bug if any.

Right, and I said that in the mail you're quoting.

> It actually fixes a kernel panic bag when iocb.users count becomes
> incorrect. The bag " Kernel BUG at fs/aio.c:509" is there because
> aio_run_iocb() have not a chance to differ real EIO and
> EIO which is actually means EAGAYN or EIOCBRETRY.

Yes, I understand the bug you're trying to fix.  You're introducing  
other bugs with the patch.  It will not be merged.

> It is interesting that I've not seen any EIOCBQUEUED returned
> to aio_run_iocb() during 5 hours aiostress running.

What arguments are you running aio-stress with?  -EIOCBQUEUED is only  
used for O_DIRECT, and then only in certain circumstances.

- z
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