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From: Shakeel Butt Date: Fri, 2 May 2025 16:40:53 -0700 X-Gmail-Original-Message-ID: X-Gm-Features: ATxdqUFYlzigjs82EjrKHhRoE1vnHFOUKUQOL1fcOT0yG0kjvzFLy9bjym4kI_8 Message-ID: Subject: Re: [PATCH v2 3/3] memcg: no irq disable for memcg stock lock To: Alexei Starovoitov Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Alexei Starovoitov , linux-mm , "open list:CONTROL GROUP (CGROUP)" , bpf , LKML , Meta kernel team , Vlastimil Babka , Sebastian Andrzej Siewior Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 4E77E40004 X-Stat-Signature: nett4nfgq8yx7ntipjmd4h5a91qk34fx X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1746229269-534487 X-HE-Meta: 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 OH1dBbXC vx8ltjafvHGa5bORumBpVbkFpS9A6r9AceuL9Ni9nG9z1Bt2jijaIhBGhE9i1l32UA+jZxYB3uN+c3gMf+nYMESZyFGSlSHPrYVcP17shR32r4VlPJ9jvnd0n4Dod9SkxF54E3eBD8I+BcsHVgn5BmK/sK/XbCCL5N6v6tVExWPVG51jTwTI1SnSLAJcdg+aP/jukYxTzQiMtIDvqneb6XSjAxojP/Z89qYrijfgDW572Ygo= 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: On Fri, May 2, 2025 at 4:28=E2=80=AFPM Alexei Starovoitov wrote: [...] > > > > > > I don't think it works. > > > When there is a normal irq and something doing regular GFP_NOWAIT > > > allocation gfpflags_allow_spinning() will be true and > > > local_lock() will reenter and complain that lock->acquired is > > > already set... but only with lockdep on. > > > > Yes indeed. I dropped the first patch and didn't fix this one > > accordingly. I think the fix can be as simple as checking for > > in_task() here instead of gfp_mask. That should work for both RT and > > non-RT kernels. > > Like: > if (in_task()) > local_lock(...); > else if (!local_trylock(...)) > > Most of the networking runs in bh, so it will be using > local_trylock() path which is probably ok in !PREEMPT_RT, > but will cause random performance issues in PREEMP_RT, > since rt_spin_trylock() will be randomly failing and taking > slow path of charging. It's not going to cause permanent > nginx 3x regression :), but unlucky slowdowns will be seen. > A task can grab that per-cpu rt_spin_lock and preempted > by network processing. Does networking run in bh for PREEMPT_RT as well? I think I should get networking & RT folks opinion on this one. I will decouple this irq patch from the decoupling lock patches and start a separate discussion thread.