linux-kernel - Re: [PATCH] squashfs: avoid bio_alloc() failure with 1Mbyte blocks

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Date:   Tue, 18 Aug 2020 20:13:26 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Guenter Roeck <groeck@...gle.com>
Cc:     Phillip Lougher <phillip@...ashfs.org.uk>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Philippe Liard <pliard@...gle.com>, hch@....de,
        adrien+dev@...ischi.me, Guenter Roeck <groeck@...omium.org>,
        Daniel Rosenberg <drosen@...gle.com>,
        Nicolas Prochazka <nicolas.prochazka@...il.com>,
        Tomoatsu Shimada <shimada@...brix.com>
Subject: Re: [PATCH] squashfs: avoid bio_alloc() failure with 1Mbyte blocks

On Fri, 14 Aug 2020 21:30:33 -0700 Guenter Roeck <groeck@...gle.com> wrote:

> On Fri, Aug 14, 2020 at 8:57 PM Phillip Lougher <phillip@...ashfs.org.uk> wrote:
> >
> > This is a regression introduced by the "migrate from ll_rw_block usage
> > to BIO" patch.
> >
> > Bio_alloc() is limited to 256 pages (1 Mbyte).   This can cause a
> > failure when reading 1 Mbyte block filesystems.  The problem is
> > a datablock can be fully (or almost uncompressed), requiring 256
> > pages, but, because blocks are not aligned to page boundaries, it
> > may require 257 pages to read.
> >
> > Bio_kmalloc() can handle 1024 pages, and so use this for the
> > edge condition.
> >
> > Reported-by: Nicolas Prochazka <nicolas.prochazka@...il.com>
> > Reported-by: Tomoatsu Shimada <shimada@...brix.com>
> > Signed-off-by: Phillip Lougher <phillip@...ashfs.org.uk>
> 
> Fixes: 93e72b3c612a ("squashfs: migrate from ll_rw_block usage to BIO")
> Reviewed-by: Guenter Roeck <groeck@...omium.org>

Thanks.  I added cc:stable also.