linux-kernel - Re: [PATCH v4] scsi: ufs: Cleanup completed request without interrupt notification

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Message-ID: <97f1dfb0-41b6-0249-3e82-cae480b0efb6@acm.org>
Date:   Thu, 30 Jul 2020 21:06:41 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Stanley Chu <stanley.chu@...iatek.com>,
        Avri Altman <Avri.Altman@....com>
Cc:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "alim.akhtar@...sung.com" <alim.akhtar@...sung.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kuohong.wang@...iatek.com" <kuohong.wang@...iatek.com>,
        "peter.wang@...iatek.com" <peter.wang@...iatek.com>,
        "chun-hung.wu@...iatek.com" <chun-hung.wu@...iatek.com>,
        "andy.teng@...iatek.com" <andy.teng@...iatek.com>,
        "chaotian.jing@...iatek.com" <chaotian.jing@...iatek.com>,
        "cc.chou@...iatek.com" <cc.chou@...iatek.com>
Subject: Re: [PATCH v4] scsi: ufs: Cleanup completed request without interrupt
 notification

On 2020-07-30 18:30, Stanley Chu wrote:
> On Mon, 2020-07-27 at 11:18 +0000, Avri Altman wrote:
>> Looks good to me.
>> But better wait and see if Bart have any further reservations.
> 
> Would you have any further suggestions?

Today is the first time that I took a look at ufshcd_abort(). The
approach of that function looks wrong to me. This is how I think that a
SCSI LLD abort handler should work:
(1) Serialize against the completion path
(__ufshcd_transfer_req_compl()) such that it cannot happen that the
abort handler and the regular completion path both call
cmd->scsi_done(cmd) at the same time. I'm not sure whether an existing
synchronization object can be used for this purpose or whether a new
synchronization object has to be introduced to serialize scsi_done()
calls from __ufshcd_transfer_req_compl() and ufshcd_abort().
(2) While holding that synchronization object, check whether the SCSI
command is still outstanding. If so, submit a SCSI abort TMR to the device.
(3) If the command has been aborted, call scsi_done() and return
SUCCESS. If aborting failed and the command is still in progress, return
FAILED.

An example is available in srp_abort() in
drivers/infiniband/ulp/srp/ib_srp.c.

Bart.