Re: [PATCH mm-hotfixes] mm/zswap: add missing kunmap_local()

[SeongJae Park]

On Mon, 16 Mar 2026 14:01:22 +0000 "Lorenzo Stoakes (Oracle)" <ljs@xxxxxxxxxx> wrote:

> Commit e2c3b6b21c77 ("mm: zswap: use SG list decompression APIs from
> zsmalloc") updated zswap_decompress() to use the scatterwalk API to copy
> data for uncompressed pages.
> 
> In doing so, it mapped kernel memory locally for 32-bit kernels using
> kmap_local_folio(), however it never unmapped this memory.
> 
> This resulted in the linked syzbot report where a BUG_ON() is triggered due
> to leaking the kmap slot.
> 
> This patch fixes the issue by explicitly unmapping the established kmap.

Nice catch, thank you for this fix!

> 
> Reported-by: syzbot+fe426bef95363177631d@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://lore.kernel.org/all/69b75e2c.050a0220.12d28.015a.GAE@xxxxxxxxxx
> Fixes: e2c3b6b21c77 ("mm: zswap: use SG list decompression APIs from zsmalloc")
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@xxxxxxxxxx>

Reviewed-by: SeongJae Park <sj@xxxxxxxxxx>


Thanks,
SJ

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