linux-kernel - Re: [PATCH v4] block: make sure big bio is splitted into at most 256 bvecs

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Date:   Wed, 24 Aug 2016 00:38:00 -0800
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     Ming Lei <ming.lei@...onical.com>
Cc:     Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
        Eric Wheeler <bcache@...ts.ewheeler.net>,
        Sebastian Roesner <sroesner-kernelorg@...sner-online.de>,
        "4.3+" <stable@...r.kernel.org>, Shaohua Li <shli@...com>,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v4] block: make sure big bio is splitted into at most 256
 bvecs

On Tue, Aug 23, 2016 at 09:49:45PM +0800, Ming Lei wrote:
> After arbitrary bio size is supported, the incoming bio may
> be very big. We have to split the bio into small bios so that
> each holds at most BIO_MAX_PAGES bvecs for safety reason, such
> as bio_clone().
> 
> This patch fixes the following kernel crash:
> 
> > [  172.660142] BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
> > [  172.660229] IP: [<ffffffff811e53b4>] bio_trim+0xf/0x2a
> > [  172.660289] PGD 7faf3e067 PUD 7f9279067 PMD 0
> > [  172.660399] Oops: 0000 [#1] SMP
> > [...]
> > [  172.664780] Call Trace:
> > [  172.664813]  [<ffffffffa007f3be>] ? raid1_make_request+0x2e8/0xad7 [raid1]
> > [  172.664846]  [<ffffffff811f07da>] ? blk_queue_split+0x377/0x3d4
> > [  172.664880]  [<ffffffffa005fb5f>] ? md_make_request+0xf6/0x1e9 [md_mod]
> > [  172.664912]  [<ffffffff811eb860>] ? generic_make_request+0xb5/0x155
> > [  172.664947]  [<ffffffffa0445c89>] ? prio_io+0x85/0x95 [bcache]
> > [  172.664981]  [<ffffffffa0448252>] ? register_cache_set+0x355/0x8d0 [bcache]
> > [  172.665016]  [<ffffffffa04497d3>] ? register_bcache+0x1006/0x1174 [bcache]

Acked-by: Kent Overstreet <kent.overstreet@...il.com>