linux-ext4 - [Bug 201631] WARNING: CPU: 11 PID: 29593 at fs/ext4/inode.c:3927 .ext4_set_page

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Date:   Thu, 20 Dec 2018 07:49:03 +0000
From:   bugzilla-daemon@...zilla.kernel.org
To:     linux-ext4@...r.kernel.org
Subject: [Bug 201631] WARNING: CPU: 11 PID: 29593 at fs/ext4/inode.c:3927
 .ext4_set_page_dirty+0x70/0xb0

https://bugzilla.kernel.org/show_bug.cgi?id=201631

--- Comment #28 from Jan Kara (jack@...e.cz) ---
(In reply to Benjamin Herrenschmidt from comment #24)
> Out of curiosity, how does this work in the context of pages that are GUPed
> either by a driver or by KVM when using file backed guest memory ?
> 
> GUP will not "see" the mkclean or attempt at making read only...

That's a good question :) Well behaved GUP users use mmu notifiers as Aneesh
wrote to "see" mkclean. Badly behaved GUP users (and there's quite a few of
them) don't and that can result in kernel crashes, data loss, or checksum
failures in storage stack. The latest discussion on this topic is here if
you're interested: https://lwn.net/Articles/774411/

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