linux-kernel - RE: [PATCH v2 4/5] cramfs: add mmap support

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Message-ID: <SG2PR06MB1165FE414425AFD1C64E7CD78A9F0@SG2PR06MB1165.apcprd06.prod.outlook.com>
Date:   Tue, 29 Aug 2017 19:38:03 +0000
From:   Chris Brandt <Chris.Brandt@...esas.com>
To:     Nicolas Pitre <nicolas.pitre@...aro.org>,
        Al Viro <viro@...IV.linux.org.uk>
CC:     "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-embedded@...r.kernel.org" <linux-embedded@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 4/5] cramfs: add mmap support

On Monday, August 28, 2017, Nicolas Pitre wrote:
> OK I moved the lock promotion right at the beginning _before_ validating
> the split point. Also got a reference on the file to make sure that
> hasn't changed too.
> 
> > While we are at it, what happens if you mmap 120Kb, then munmap() the
> middle
> > 40Kb.  Leaving two 40Kb VMAs with 40Kb gap between them, that is.  Will
> your
> > ->vm_private_data be correct for both?
> 
> It wouldn't, but I now changed it to contain absolute values so now it
> will. And if the split point lands in the hole then the code just
> readjusts the pgoff at the beginning of the remaining part.
> 
> Here's the revised patch:


For whatever it's worth, as soon as I moved to 4.13-rc7,
CONFIG_CRAMFS_PHYSMEM=y crashes my XIP_KERNEL system before it can even 
get to any console output.

(both the old patch and the new patch)

If CONFIG_CRAMFS_PHYSMEM is not set, my XIP system boots fine.

However, if I boot -rc7 as a uImage, the new patch works just as good as
the old patch.

(mounting after boot, or booting with rootfstype=cramfs_physmem)


I guess I'll have to figure out what happened between -rc4 and -rc7.
Damn!


Chris