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Howlett" , Lorenzo Stoakes , Lu Baolu , "H. Peter Anvin" , Shakeel Butt , Suren Baghdasaryan , Thomas Gleixner , Toshi Kani , Vishal Moola , Vlastimil Babka , Will Deacon , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH 1/5] x86/mm/pat: introcude cpa_lock() and cpa_unlock() Message-ID: References: <20260728-cpa-fixes-v1-0-2ed2352300b3@kernel.org> <20260728-cpa-fixes-v1-1-2ed2352300b3@kernel.org> <20260728142108.GW751831@noisy.programming.kicks-ass.net> <20260728143135.GG651302@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260728143135.GG651302@noisy.programming.kicks-ass.net> X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: D948A180011 X-Stat-Signature: rcxh73jejpi4mqb3z9bap4kccwtwnatf X-HE-Tag: 1785250003-617232 X-HE-Meta: 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 NEMF8+IQ 7ipukG00+vkGz0ysdW5PNm4KuJkhVBO6IRLrub3GlQq/3/7RAv6Q1Os5ZOhh36b0oli0GnOkTiRPBrRwm0gLBC1Y+Eqn5i4I13pKy/0HpRwYCR8LXywL6fBRioCE2z6wzCmjtHPhu+5fP6fadhuSEeABJ84nf5kNHx4ECu8ussOgc/wGUduQO8c12xXabfo0W43qxE2DUH6433DqXXzy6LCJBjko+Wq2RnbfJ9FSRIuNI/MebqynLaOOFidPuYzs/8wPUtyJTcdLxs0r0/LYVZz3J5uqum8mAvFQNfNMU8XfJS8g+0FEJndkRJqWSrS5C4ZzRhwgKrqtEo481PSf1v4SwKzNOcvbyYAHgzINQLm3ggl9aOIMpE2wDmNGosyQ2uz0p Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jul 28, 2026 at 04:31:35PM +0200, Peter Zijlstra wrote: > On Tue, Jul 28, 2026 at 07:30:27AM -0700, Dave Hansen wrote: > > On 7/28/26 07:21, Peter Zijlstra wrote: > > > There was already a patch merged that removed the shole debug_pagealloc > > > exception. Is that not better? > > > > As I'm scanning through email this morning, there's another issue that > > popped up with that patch. It's causing hangs on boot. > > > > It's looking like debug pagealloc not taking the lock is actually > > functional, not an optimization. Although, I hesitate to say > > "functional" and would prefer to use much less nice words to describe it. > > Yeah, lets figure out why that is before we retain this wart ;-) As Lorenzo said: __kernel_map_pages() can be called from irq context: < GFP_ATOMIC context > kfree() or whatever -> ... -> __free_pages_prepare() -> debug_pagealloc_unmap_pages() -> __kernel_map_pages() -> __change_page_attr_set_clr() -> cpa_lock -- Sincerely yours, Mike.