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b=onaCm5sYCrFpmf1zu9J/x02WZtd4jpgTMIHMd3pdzw7+MDI8z2TbRN0UMATB5SX8t RejjVNolNajkTFy9C1LnW/D+StxC13R84Onk4/JaDXvhscWMYL3LOsfCQWjpkB02XT F54R4ADnwdLCkmXK7FmaDkJ1jKuYzxHmHRtS0AR+g6HZoqWcphmzfbnbTbIzlyzlK8 GIDeCpcFGnoOEqxKyC0cJeS0zxU/txv2JXb4IMFKK9me9ScQVxO5Y3FfehUrGKiS4T qvUsqNim/fwniei6C+IO4Dlsi764Mhx0DYbvOHoAcRnbSRIom0tmtlYKKZ2YkEWEUr WjdAkGm34ih0Q== Date: Mon, 16 Mar 2026 15:49:23 +0000 From: "Lorenzo Stoakes (Oracle)" To: Yosry Ahmed Cc: Andrew Morton , Johannes Weiner , 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: <59b849b9-87ff-48f7-94fb-363d5f54d8f4@lucifer.local> References: <20260316140122.339697-1-ljs@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: AA8D8C000C X-Stat-Signature: o66utgj8pnar737dmteewf8i45i7frok X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1773676167-279741 X-HE-Meta: U2FsdGVkX1/HzM2jCsO9bgCBPpeMzd1V7wmeoxxRc0ITjpwsjrweaL16TOnebLMYmT6WnIEAY+5+rBYHvWwVCPiHl/X7o1kjaaS5M0NgzyxrYoGilR2h+vIDR0Ye1aIk57z20JkYldGYsfQEC/x0cU4JwDtciGirZBY0OMBerR68qAb/QE9FH5j8IXNb6e/UYSDVKsX3JyNDiXhbfK/mQKxsynAVL+Lz6KTuFTyJs7NBomNvNT3WXhexF8quCRHck39skW75GqIb1/c8vp7IycCCuoV/prsStoFlAGop68tsumxPs4g7GgrbRJRgs50zKKSunhiu3enByVoPp29BPDqtgirYQFZajAT+Z6kk0n/ieGHNCZOKcqTy6eXa3QqoxemBo4vRhTCt5wSmLkDAaF0zoz6RdzVIRoDwz5b/9AXAaNT9m4r4brgDq5YXi7WXvwDJGLP7mMUBmgXmaZlQ5jxk02/7TvqLHQvPnkSctfyy5XGS6mWFyp+P16FbOmMHWf0S0VN+Ewef+lw2iBZxvPePKh/cNKtBcvbbh324D3AjBQ/LOqlqo/7/o6mWZQIyCVMaHeeOInq0jF00pOKRerwgZl/WEWSYRkUoaZZA1RvcyODSpFvmqZs/XU0iaDrGk0Vj6R2jBY5Sm7hYQj19hXABD99h0W8xwukUxojfqj8PcqdHudysziKx4esipe5Am+tXszCCAkbF+FmIZaqsvGzKTBX+U1TaENKRFwxD8m+djcmcG1SAsx4MOUlicVP4hgwx3wL3g+VnEG3/875A/hS4AthjIo2GjfJ3C+L4PCmmMADl72YqWRYSjXpOI2pTvzLRARpeq5sC9KDDNgwo0FXRgYkBqeNUBy6OU9BSE5TC1Lh9olyKLqpJhbq1ZJVFXsoKb/CmtxHSjk7cal2vTL1UfDhs3Itqg0okEhBSKiNz4eOyxvK1Fvi9xZnRAFTp+UVP8rv+4t0ZGZegq8T yf4zQMlZ RNGejfnaEI+HNxj1+lBplcBbTMFeCTcl7AZwtjJndK1Van2Lge6hGuxI07pkbj4AYL0FUGvBzG5lxqHB80yrg5ZjnSbkhOweGKm2QoTaTtTkYB6020oepd+sRWdUNHlX2MGhjP3x/HjeQIJEiK1crNrssyQ8iJSa9IT0Wju8gsrPM2jjSreIHVZcspWETykP1rZ0BI/bNaYa0dc8K1rsjo47SiGyze/Yk3kOdK9Tcwp5HVm8H2yLJVEkvH4JMUH+bOnaKFwY9pwVTGUD2doq0AzraR81pPlxQFC/d1fzKeQ8bkMM8Bvhw8w/Cvnr+7dH8vwAZMuUTlHkhJKlv0aUOAo0H9ZnAhip2iaCN62vJOzj9jSA= 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 02:52:24PM +0000, Yosry Ahmed wrote: > 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) > > Oh thanks for catching that, not sure how I ended up doing that tbh.. Don't worry I've made FAR worse mistakes in some of my patches, believe me :) easily done. > > Anyway, LGTM: > > Acked-by: Yosry Ahmed Thanks! Cheers, Lorenzo > > > --- > > mm/zswap.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/mm/zswap.c b/mm/zswap.c > > index e6ec3295bdb0..499520f65ff0 100644 > > --- a/mm/zswap.c > > +++ b/mm/zswap.c > > @@ -942,9 +942,14 @@ static bool zswap_decompress(struct zswap_entry *entry, struct folio *folio) > > > > /* zswap entries of length PAGE_SIZE are not compressed. */ > > if (entry->length == PAGE_SIZE) { > > + void *dst; > > + > > WARN_ON_ONCE(input->length != PAGE_SIZE); > > - memcpy_from_sglist(kmap_local_folio(folio, 0), input, 0, PAGE_SIZE); > > + > > + dst = kmap_local_folio(folio, 0); > > + memcpy_from_sglist(dst, input, 0, PAGE_SIZE); > > dlen = PAGE_SIZE; > > + kunmap_local(dst); > > } else { > > sg_init_table(&output, 1); > > sg_set_folio(&output, folio, PAGE_SIZE, 0); > > -- > > 2.53.0