Re: [PATCH v2] mm/mmap: Regression fix for unmapped_area{_topdown}

[Michael Keyes]

On 29.04.23 15:32, Tad wrote:
> This reintroduces the issue described in
> https://lore.kernel.org/linux-mm/cb8dc31a-fef2-1d09-f133-e9f7b9f9e77a@xxxxxxxx/
Yes, I also ran into this (even though I'd somehow missed it the
previous time).

Apparently the issue arises at mm/mmap.c:1582, where low_limit is set to
vm_end_gap(tmp). Occasionally, this returns a 64-bit address (e.g.
0x7fedea581000), which is obviously greater than high_limit for a 32-bit
mmap, and causes the next call to mas_empty_area() to fail.

I'm not sure why vm_end_gap(tmp) occasionally returns a 64-bit address,
or if the best solution is to just check for this and skip the retry if
it occurs…

-- 
Michael