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

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Date:   Wed, 23 Jan 2019 16:40:31 +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 #47 from Jan Kara (jack@...e.cz) ---
OK, so it seems to be more and more clear that PPC indeed has some race in page
table updates. What I can see in the latest report is:

Clean page (index 92, ino 681741, i_size 828368, flags 7fff0000002016, mapcount
1) with dirty PTE (pte_val c0000005f7fae186) on unmap! Vma flags fb, pgoff 0,
file ino 681741
...
page 92: b_state 21, b_blocknr 2801084, b_mapped 1452389112002, b_mapped2 0,
b_cleaned 1452396217779, now 1452400395514

So "Vma flags fb" shows its a normal shared, writeable file mapping. Page is
somewhere in the middle of the file (file size is 828368, page is at offset
376832). The page has been writeably mapped 11ms ago (you are using ext2
filesystem which was confusing my previous debug attempts so only this one has
shown proper times) and written back 4ms ago (which should have writeprotected
the pte) but we still have writeable pte now on which the assertion hits. So
either page_mkclean() failed to clear the PTE or someone created new writeable
PTE without telling ext4.

I'll attach a new version of debug patch to distinguish these two cases.

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