[Bug 112012] kernel BUG at fs/ext4/inode.c:2721!

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=112012

--- Comment #1 from Chris Wilson <chris at chris-wilson.co.uk> ---
(In reply to Robert Holmes from comment #0) 
> Now, the reason I am reporting this on this bug tracker is that I've
> bisected this issue (more precisely, the first WARNING right after boot) to
> the following commit:
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/
> ?h=linux-5.3.y&id=0bd6cb6b58f7332c61cef2e4ae48db1ca9910b6b

Yikes. That shows that code was inherently more buggy than I thought, as it was
causing us to drop writes to pages we didn't own (but thought we did).

The root cause of the warn and ext4 bug is the lack of lock_page around
set_page_dirty in userptr_put_pages. We tried putting a lock there, but we
recurse into userptr_put_pages from underneath locked pages...

There is a plan afoot to replace this interface with HMM in the hope that it
makes the integration between the GPU and user pages much nicer and in the
process resolve these mistakes.

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