linux-kernel - Re: [PATCH] block: don't make BLK_DEF_MAX

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Date:	Tue, 29 Mar 2016 23:51:51 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Shaohua Li <shli@...com>
Cc:	Christoph Hellwig <hch@...radead.org>, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, axboe@...com, Kernel-team@...com,
	"4.2+" <stable@...r.kernel.org>, Ming Lei <ming.lei@...onical.com>
Subject: Re: [PATCH] block: don't make BLK_DEF_MAX_SECTORS too big

On Tue, Mar 29, 2016 at 03:01:10PM -0700, Shaohua Li wrote:
> The problem is bcache allocates a big bio (with bio_alloc). The bio is
> split with blk_queue_split, but it isn't split to small size because
> queue limit. the bio is cloned later in md, which uses bio_alloc_bioset.
> bio_alloc_bioset itself can't allocate big size bio.

bcache should be fixed to not allocate larger than allowed bios then.
And handling too large arguments to bio_alloc_bioset is still useful to
avoid the checks in the callers and make it robust.