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Tue, 22 Aug 2023 14:37:14 -0700 (PDT) MIME-Version: 1.0 References: <20230817-free_pcppages_bulk-v1-0-c14574a9f80c@kernel.org> <20230821103225.qntnsotdzuthxn2y@techsingularity.net> In-Reply-To: From: Alexei Starovoitov Date: Tue, 22 Aug 2023 14:37:02 -0700 Message-ID: Subject: Re: [PATCH RFC 0/2] mm/page_alloc: free_pcppages_bulk safeguard To: Chris Li Cc: Mel Gorman , Andrew Morton , Kemeng Shi , baolin.wang@linux.alibaba.com, Michal Hocko , David Hildenbrand , Matthew Wilcox , linux-mm , Namhyung Kim , Greg Thelen , LKML , John Sperbeck , Huang Ying , Alexei Starovoitov Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 01440120017 X-Rspam-User: X-Stat-Signature: 8drn3nrrnjhzato79mmzxfobob9rge48 X-Rspamd-Server: rspam03 X-HE-Tag: 1692740235-570677 X-HE-Meta: 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 Wsoe98ej 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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: On Tue, Aug 22, 2023 at 2:34=E2=80=AFPM Chris Li wrote: > > Hi Alexei, > > On Tue, Aug 22, 2023 at 11:57=E2=80=AFAM Alexei Starovoitov > wrote: > > > > On Tue, Aug 22, 2023 at 10:48=E2=80=AFAM Chris Li w= rote: > > > > > > Hi Mel, > > > > > > Adding Alexei to the discussion. > > > > > > On Mon, Aug 21, 2023 at 3:32=E2=80=AFAM Mel Gorman wrote: > > > > > > > > On Thu, Aug 17, 2023 at 11:05:22PM -0700, Chris Li wrote: > > > > > In this patch series I want to safeguard > > > > > the free_pcppage_bulk against change in the > > > > > pcp->count outside of this function. e.g. > > > > > by BPF program inject on the function tracepoint. > > > > > > > > > > I break up the patches into two seperate patches > > > > > for the safeguard and clean up. > > > > > > > > > > Hopefully that is easier to review. > > > > > > > > > > Signed-off-by: Chris Li > > > > > > > > This sounds like a maintenance nightmare if internal state can be a= rbitrary > > > > modified by a BPF program and still expected to work properly in al= l cases. > > > > Every review would have to take into account "what if a BPF script = modifies > > > > state behind our back?" > > > > Where did this concern come from? > > Since when BPF can modify arbitrary state? > > > > But I wasn't cc-ed on the original patch, so not sure what it attempts = to do. > > Maybe concern is valid. > > Sorry I did not CC you on the original patch submission. I should. > > Here is the link for the 1/2 patch, which has the step to reproduce. > > https://lore.kernel.org/linux-mm/20230817-free_pcppages_bulk-v1-1-c14574a= 9f80c@kernel.org/ > > It is using an older version of the BPF program. That spinlock > allocation was fixed > in commit c66a36af7ba3a628. No. It was a temp workaround. It was fixed on bpf local storage side later.