Re: [PATCH 5.10 0/2] mm/truncate: fix issue in ext4_set_page_dirty()

[Roman Smirnov]

On Thu, 11 Jan 2024 15:31:12 +0000, Matthew Wilcox wrote:

> I do not understand the crash, and I do not understand why this patch
> would fix it.  Can you explain either?

The WARNING appears in the following location:
https://elixir.bootlin.com/linux/v5.10.205/source/fs/ext4/inode.c#L3693

Reverse bisection pointed at the 2nd patch as a fix, but after 
backporting this patch to 5.10 branch I still hit the WARNING.
I noticed that there was some missing code compared to the original
patch:

if (folio_has_private(folio) && !filemap_release_folio(folio, 0))
         return 0;

Then I found a patch with this code before using folio, applied it,
and tests showed the WARNING disappeared. I also used the linux test
project to make sure nothing was broken. I'll try to dig a little
deeper and explain the crash.

Thanks for the reply.