linux-kernel - RE: [PATCH] storvsc: do not assume SG list is continuous when doing bounce buffers (for 4.1 stable only)

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Message-ID: <MWHPR21MB0190D1C8C3FAF25AE283ABCFCE840@MWHPR21MB0190.namprd21.prod.outlook.com>
Date:   Tue, 22 Aug 2017 19:11:04 +0000
From:   Long Li <longli@...rosoft.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "James E.J. Bottomley" <JBottomley@...n.com>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH] storvsc: do not assume SG list is continuous when doing
 bounce buffers (for 4.1 stable only)

 
> Wouldn't it make sense to backport the changes to set the virt_boundary
> (which probably still is the SG_GAPS flag in such an old kernel)?

We can make storvsc use SG_GAPS. But the following patch is missing in 4.1 stable block layer to make this work on some I/O situations. Backporting is more difficult and affect other code.

commit 5e7c4274a70aa2d6f485996d0ca1dad52d0039ca
Author: Jens Axboe <axboe@...com>
Date:   Thu Sep 3 19:28:20 2015 +0300

    block: Check for gaps on front and back merges
    
    We are checking for gaps to previous bio_vec, which can
    only detect back merges gaps. Moreover, at the point where
    we check for a gap, we don't know if we will attempt a back
    or a front merge. Thus, check for gap to prev in a back merge
    attempt and check for a gap to next in a front merge attempt.
    
    Signed-off-by: Jens Axboe <axboe@...com>
    [sagig: Minor rename change]
    Signed-off-by: Sagi Grimberg <sagig@...lanox.com>