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

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Message-ID: <bug-201631-13602-nAwS8MyKPL@https.bugzilla.kernel.org/>
Date:   Sun, 16 Dec 2018 20:47:42 +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 #11 from Benjamin Herrenschmidt (benh@...nel.crashing.org) ---
Jan, I don't know for sure what problems triggers it here, but there definitely
is a HW bug on POWER9 with the "NestMMU" (the MMU that services coprocessors
and the nvlink), which can cause a dirty bit to be set on a read-only PTE if it
races with the PTE update & invalidation.

It was "assumed" this was ok. If not I don't know how to work around it.

However, at least in the above cases, I don't see how we would be setting dirty
if we don't have RW access permission. A PowerMac G5 uses the hash MMU, we set
dirty atomically with checking the PTE permission when hashing a PTE in.

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