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d=linutronix.de; s=2020e; t=1660836175; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8yxb0BK/v/93Xq0pa1I9UCRiP9ec/brO7gpNu4/9X1I=; b=dmenoKVG6VL28Mv4WKSd3gfipU49QQ0XlOgJfkhoKvR2lKtquKwtrYIEc2TVlo2m8sL8GC xaS/J1l+pxZr3WCg== From: Sebastian Andrzej Siewior To: Vlastimil Babka Cc: Christoph Lameter , linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Steven Rostedt , Linus Torvalds , Matthew Wilcox , Andrew Morton , David Rientjes , Joonsoo Kim , Pekka Enberg , linux-mm@kvack.org Subject: Re: [PATCH 1/9] slub: Make PREEMPT_RT support less convoluted Message-ID: References: <20220817162703.728679-1-bigeasy@linutronix.de> <20220817162703.728679-2-bigeasy@linutronix.de> <5679405a-b3c3-6dc5-783f-7ebeda7c9bf0@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <5679405a-b3c3-6dc5-783f-7ebeda7c9bf0@suse.cz> ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=linutronix.de header.s=2020 header.b=N0sOwP6Y; dkim=pass header.d=linutronix.de header.s=2020e header.b=dmenoKVG; spf=pass (imf02.hostedemail.com: domain of bigeasy@linutronix.de designates 193.142.43.55 as permitted sender) smtp.mailfrom=bigeasy@linutronix.de; dmarc=pass (policy=none) header.from=linutronix.de ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660856765; a=rsa-sha256; cv=none; b=pSqm3it1sIOrTf9tYu0nTBjlTZl+EuuLvQJc2LBQBUXFF8j5jdu3KV/owrXg8n1RDGJ3Qq vYtoCAQEpfyC8bQqfw+G75NjxmFmhX8k3kGiTgF56kORiRocEwcd/TmLnPdQ+FZ99nbJ7o aockkbsuXA7zMP2q2ChaXyFwnqcvRKs= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660856765; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=8yxb0BK/v/93Xq0pa1I9UCRiP9ec/brO7gpNu4/9X1I=; b=0ehsFk3KvwAhA5o9OARJCmLgDtFBA4roZSedVNni8Hk2eJEQnokbkTJeyWz5XSLKzQLFFI vvhbkAO49IIEBKo6leXuqprvQL+uuv4sTniz9CKwlz8ER2IBK+bPIcJdmcbT1GBn9Anyyo PkKd5isHHCRU0bNHHBPoNaNLDflQO1c= X-Rspamd-Queue-Id: 40754815D5 Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=linutronix.de header.s=2020 header.b=N0sOwP6Y; dkim=pass header.d=linutronix.de header.s=2020e header.b=dmenoKVG; spf=pass (imf02.hostedemail.com: domain of bigeasy@linutronix.de designates 193.142.43.55 as permitted sender) smtp.mailfrom=bigeasy@linutronix.de; dmarc=pass (policy=none) header.from=linutronix.de X-Rspamd-Server: rspam01 X-Rspam-User: X-Stat-Signature: a3w14eewa4g79kamch489metiqs8qu6m X-HE-Tag: 1660856764-226748 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 2022-08-18 16:37:06 [+0200], Vlastimil Babka wrote: > > The slub fastpath does not interfere with slow path operations and the > > That's true on !PREEMPT_RT because a slowpath operation under > local_lock_irqsave() will disable interrupts, so there can't be a > fastpath operation in an interrupt handler appearing in the middle of a > slowpath operation. > > On PREEMPT_RT local_lock_irqsave() doesn't actually disable interrupts, > so that can happen. IIRC we learned that the hard way when Mike > Galbraith was testing early versions of my PREEMPT_RT changes for SLUB. I think the point is that local_lock_irqsave() does not disable preemption. So the lock owner (within the local_lock_irqsave() section) can be preempted and another task can use the fast path which does not involve the lock and things go boom from here. Sebastian