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b=r1ePCVIEMutoRd7UrDkWj2iYyVFGYbgLcHeSq9obJ4o4zzzwK3u4nxTihrF8eZ1yq sfnuFjVWVf78FPKIU2e5mF59xnqWoRuYfTRYV2njrfu0kiUILM+7dub00TiAKJplOu ngwhrE3y+SLoH095RDwg9P65PpQqcwuApLlWTgfX+Ck3rKSqe+7nEi3Pkzk2cG5zdI TsAIS4ceXMHebQD+72i+fpNySaV7B33uhk1AdjtbOhggpGGxK/dm5f59yfOCp0X1Wj uBSwsMwGXw0xoK3z0qEHuOggsU8fHqsZTSiDKPpse23MgOtaWsHt4yUiL9MT2Zj9eX cJxDDq6v0NNZA== Date: Thu, 9 Nov 2023 09:51:18 -0800 From: Josh Poimboeuf To: Steven Rostedt Cc: Ankur Arora , linux-kernel@vger.kernel.org, tglx@linutronix.de, peterz@infradead.org, torvalds@linux-foundation.org, paulmck@kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, jgross@suse.com, andrew.cooper3@citrix.com, mingo@kernel.org, bristot@kernel.org, mathieu.desnoyers@efficios.com, geert@linux-m68k.org, glaubitz@physik.fu-berlin.de, anton.ivanov@cambridgegreys.com, mattst88@gmail.com, krypton@ulrich-teichert.org, David.Laight@ACULAB.COM, richard@nod.at, mjguzik@gmail.com, Jiri Kosina , Miroslav Benes , Petr Mladek , Joe Lawrence , live-patching@vger.kernel.org Subject: Re: [RFC PATCH 07/86] Revert "livepatch,sched: Add livepatch task switching to cond_resched()" Message-ID: <20231109175118.olggitpaltz47n3b@treble> References: <20231107215742.363031-1-ankur.a.arora@oracle.com> <20231107215742.363031-8-ankur.a.arora@oracle.com> <20231107181609.7e9e9dcc@gandalf.local.home> <20231109172637.ayue3jexgdxd53tu@treble> <20231109123147.2bb11809@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20231109123147.2bb11809@gandalf.local.home> X-Stat-Signature: qwu4ux6um3ujbq3k9mpe5kx8qezmqwgf X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: E15F7180022 X-Rspam-User: X-HE-Tag: 1699552283-484790 X-HE-Meta: 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 PSrEE4jV iS+1wGPiGLs479gi4j+AMdKnOCBmimQRuXTneD64towmboc4iioalTvWCrnOx+XeoLbow67DJUVv5zIzZudukT/u8CJZZ4LNDuRneOcHJqnBRn69PXCmpKmdBOAwbU+NmhpKTf7Jx7RwYDSzXr8Qd4gpKeXd0nymyseDTswB5dn6ua1ZcHZPOc9Pf2VlbgwQyZu7XV9lBqhiAINybm7ul/6zBdVwcE1LMXNzApJXonp/fNMLmJG2gTQZiriYvC2ibxY2X0S4yYDfij0V7eCmDnfkRFSVLKNDrGMiYjiX7oFn/r9EOu2ccyejReyqSkcTFH/jo 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 Thu, Nov 09, 2023 at 12:31:47PM -0500, Steven Rostedt wrote: > On Thu, 9 Nov 2023 09:26:37 -0800 > Josh Poimboeuf wrote: > > > On Tue, Nov 07, 2023 at 06:16:09PM -0500, Steven Rostedt wrote: > > > On Tue, 7 Nov 2023 13:56:53 -0800 > > > Ankur Arora wrote: > > > > > > > This reverts commit e3ff7c609f39671d1aaff4fb4a8594e14f3e03f8. > > > > > > > > Note that removing this commit reintroduces "live patches failing to > > > > complete within a reasonable amount of time due to CPU-bound kthreads." > > > > > > > > Unfortunately this fix depends quite critically on PREEMPT_DYNAMIC and > > > > existence of cond_resched() so this will need an alternate fix. > > > > We definitely don't want to introduce a regression, something will need > > to be figured out before removing cond_resched(). > > > > We could hook into preempt_schedule_irq(), but that wouldn't work for > > non-ORC. > > > > Another option would be to hook into schedule(). Then livepatch could > > set TIF_NEED_RESCHED on remaining unpatched tasks. But again if they go > > through the preemption path then we have the same problem for non-ORC. > > > > Worst case we'll need to sprinkle cond_livepatch() everywhere :-/ > > > > I guess I'm not fully understanding what the cond rescheds are for. But > would an IPI to all CPUs setting NEED_RESCHED, fix it? If all livepatch arches had the ORC unwinder, yes. The problem is that frame pointer (and similar) unwinders can't reliably unwind past an interrupt frame. -- Josh