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Tue, 19 Mar 2024 13:32:20 -0700 (PDT) Date: Tue, 19 Mar 2024 13:32:18 -0700 From: Dennis Zhou To: Yosry Ahmed Cc: Tejun Heo , Christoph Lameter , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] percpu: clean up all mappings when pcpu_map_pages() fails Message-ID: References: <20240311194346.2291333-1-yosryahmed@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: A52661C0016 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: iji6j4k5pu16um586gk5gu4pwy4g4q4g X-HE-Tag: 1710880342-530031 X-HE-Meta: U2FsdGVkX18RbH3LWVh7KfzgdWdxVaRDV+jSp5GclHgTvdnwER6ydfBNkhXoPFK3QbzOYNUQxGKI8Y9fQ5MzTjJMV8DcwrvcFjvBOqDj4s7L/wQXqVTitLC3wcaVzf1GS6Kgc4nH+Yu4nB1t/FgLKcRXYgCSminQTBp7wahw4zopHuVNGomBvjdnGkOxOI71CESjYAGksObC5OuN9M30JY2cGokdAnzx0Wco2yC3A/Fx2Sh4koSCrqD/kEyPBWGv+WV0SDuf29474zQF3mdWxjiHczbdzczwlf+bD634Bm5rITvNpv32Enqz0wXgsNsmUXm9tYLSNz5C9jr/Df5MGtsS9mp7A9clNOBMRa/iOqI7G3jUNvnIbYmQ8FjSjvv/1JvntLOkxSrvjUlcMe23y1ZBrqhxuZ+0zVGKax5b3GH3Ca/ThqxLbLB5HbpmST77nZMwHD3QEViFTTGUr5cIzjbv8GoWFyPoHfGGhrtPWFxaFo+4pc6h/RATfgOcqjrr+kQVHaOfaY3SeIMd7B9OqOLsvG6e9UuOn9VKfDZd8yGSi1C1GwqsMxtuZaW2B3RRpfUDpW+FZ3FQxPHhMTNAdrDdYJKfx5hw/uEUiXGoRyCBtuEuiB4F40Ag8NcFaffgxXLW/Aux0AhV3xf7NFuXPP2BAsfRZENre0HQ6z4tVkvmgdP7mlavsRfqZF7YoXgXZOkXtz5gIMLX6Pz6R2RSUCJZ2vErRMpt83mwoi4xHHm6gDnzHwzH0gcPsDS3gpynR9HpxyDs8SsQapIUCh3PUcMbYWmgIa6DSjp99R03DPoGDmiteNbYYuDlAUFh2rryas1s9vSPuLymTAp9SdHxza9DGpvA2/nWrc/ivZu8UGn+K42t4OkAjgFJkZMFWuF9xXfzIaOx/6GdphC/u63RdzAn3m6MszBcwPZYvgnNmm531soiW5g06BEMCqEUSvAwstyKzh/K/aMpk09SY3l L77tnInS 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Yosry, On Tue, Mar 19, 2024 at 01:08:26PM -0700, Yosry Ahmed wrote: > On Mon, Mar 11, 2024 at 12:43 PM Yosry Ahmed wrote: > > > > In pcpu_map_pages(), if __pcpu_map_pages() fails on a CPU, we call > > __pcpu_unmap_pages() to clean up mappings on all CPUs where mappings > > were created, but not on the CPU where __pcpu_map_pages() fails. > > > > __pcpu_map_pages() and __pcpu_unmap_pages() are wrappers around > > vmap_pages_range_noflush() and vunmap_range_noflush(). All other callers > > of vmap_pages_range_noflush() call vunmap_range_noflush() when mapping > > fails, except pcpu_map_pages(). The reason could be that partial > > mappings may be left behind from a failed mapping attempt. > > > > Call __pcpu_unmap_pages() for the failed CPU as well in > > pcpu_map_pages(). > > > > This was found by code inspection, no failures or bugs were observed. > > > > Signed-off-by: Yosry Ahmed > > Any thoughts about this change? Should I resend next week after the > merge window? > Sorry for the delay. I'm looking at the code from mm/kmsan/hooks.c kmsan_ioremap_page_range(). It seems like __vunmap_range_noflush() is called on error for successfully mapped pages similar to how it's being done in percpu-vm.c. I haven't read in depth the expectations of vmap_pages_range_noflush() but on first glance it doesn't seem like percpu is operating out of the ordinary? Thanks, Dennis > > --- > > > > Perhaps the reason __pcpu_unmap_pages() is not currently being called > > for the failed CPU is that the size and alignment requirements make sure > > we never leave any partial mappings behind? I have no idea. Nonetheless, > > I think we want this change as that could be fragile, and is > > inconsistent with other callers. > > > > --- > > mm/percpu-vm.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c > > index 2054c9213c433..cd69caf6aa8d8 100644 > > --- a/mm/percpu-vm.c > > +++ b/mm/percpu-vm.c > > @@ -231,10 +231,10 @@ static int pcpu_map_pages(struct pcpu_chunk *chunk, > > return 0; > > err: > > for_each_possible_cpu(tcpu) { > > - if (tcpu == cpu) > > - break; > > __pcpu_unmap_pages(pcpu_chunk_addr(chunk, tcpu, page_start), > > page_end - page_start); > > + if (tcpu == cpu) > > + break; > > } > > pcpu_post_unmap_tlb_flush(chunk, page_start, page_end); > > return err; > > -- > > 2.44.0.278.ge034bb2e1d-goog > >