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Mon, 16 Mar 2026 08:17:33 -0700 (PDT) Date: Mon, 16 Mar 2026 11:17:32 -0400 From: Johannes Weiner To: "Lorenzo Stoakes (Oracle)" Cc: Andrew Morton , Yosry Ahmed , Nhat Pham , Chengming Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH mm-hotfixes] mm/zswap: add missing kunmap_local() Message-ID: References: <20260316140122.339697-1-ljs@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260316140122.339697-1-ljs@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: BC21E10000E X-Stat-Signature: f8wypj79m66f1pmzdo9xzew3ypjkprn3 X-HE-Tag: 1773674255-129256 X-HE-Meta: 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 FEMPSgDA 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 16, 2026 at 02:01:22PM +0000, Lorenzo Stoakes (Oracle) 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. > > Reported-by: syzbot+fe426bef95363177631d@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/69b75e2c.050a0220.12d28.015a.GAE@google.com > Fixes: e2c3b6b21c77 ("mm: zswap: use SG list decompression APIs from zsmalloc") > Signed-off-by: Lorenzo Stoakes (Oracle) Oops! Acked-by: Johannes Weiner