Re: [PATCH for v6.1 regression] mm, mremap: fix mremap() expanding vma with addr inside vma #forregzbot

[Thorsten Leemhuis <regressions@leemhuis.info>]

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On 16.12.22 17:32, Vlastimil Babka wrote:
> Since 6.1 we have noticed random rpm install failures that were tracked
> to mremap() returning -ENOMEM and to commit ca3d76b0aa80 ("mm: add
> merging after mremap resize").
> 
> The problem occurs when mremap() expands a VMA in place, but using an
> starting address that's not vma->vm_start, but somewhere in the middle.
> The extension_pgoff calculation introduced by the commit is wrong in
> that case, so vma_merge() fails due to pgoffs not being compatible.
> Fix the calculation.
> 
> By the way it seems that the situations, where rpm now expands a vma
> from the middle, were made possible also due to that commit, thanks to
> the improved vma merging. Yet it should work just fine, except for the
> buggy calculation.
> 
> Reported-by: Jiri Slaby <jirislaby@kernel.org>
> Link: https://bugzilla.suse.com/show_bug.cgi?id=1206359
> Fixes: ca3d76b0aa80 ("mm: add merging after mremap resize")

This is just for the record, the fix will soon land, but I want to have
this in the report I plan to send later.

#regzbot ^introduced ca3d76b0aa80
#regzbot from: Jiri Slaby <jirislaby@kernel.org>
#regzbot title mm: random rpm install failures that were tracked to
mremap() returning -ENOMEM
#regzbot fix mm, mremap: fix mremap() expanding vma with addr inside vma
#regzbot ignore-activity

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)

P.S.: As the Linux kernel's regression tracker I deal with a lot of
reports and sometimes miss something important when writing mails like
this. If that's the case here, don't hesitate to tell me in a public
reply, it's in everyone's interest to set the public record straight.