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[209.85.220.65]) by mx.google.com with SMTPS id x11sor16797014plv.55.2019.02.12.16.37.10 for (Google Transport Security); Tue, 12 Feb 2019 16:37:10 -0800 (PST) Received-SPF: pass (google.com: domain of aik@ozlabs.ru designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@ozlabs-ru.20150623.gappssmtp.com header.s=20150623 header.b=LcRuSAFo; spf=pass (google.com: domain of aik@ozlabs.ru designates 209.85.220.65 as permitted sender) smtp.mailfrom=aik@ozlabs.ru DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ozlabs-ru.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:openpgp:autocrypt:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=tAYunJKNMjE36dCMTjrw5wVhdez/nETVhfNMf2zU1SI=; b=LcRuSAFoFOPW4uEDKEUHWSLZ8ZQBV2SFlFrHUjTRXybOQhqgmI1o7wngQy+4A9TdNq 7jIkUjKppuFMqDEmEEbY5kvkV61aOTSH+JWE4hTKTNH/v2KPiDKzZfphzbNOPRJmC1aF 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linux-fpga@vger.kernel.org, linux-kernel@vger.kernel.org, alex.williamson@redhat.com, paulus@ozlabs.org, benh@kernel.crashing.org, mpe@ellerman.id.au, hao.wu@intel.com, atull@kernel.org, mdf@kernel.org References: <20190211224437.25267-1-daniel.m.jordan@oracle.com> <20190211224437.25267-3-daniel.m.jordan@oracle.com> <01000168e29daf0a-cb3a9394-e3dd-4d88-ad3c-31df1f9ec052-000000@email.amazonses.com> <20190212171839.env4rnjwdjyips6z@ca-dmjordan1.us.oracle.com> From: Alexey Kardashevskiy Openpgp: preference=signencrypt Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD EePO1JqpVuIow/wGud9xaPA5uvuVgRS1q7RU8otD+7VLDFzPRiRE4Jfr2CW89Ox6BF+q5ZPV /pS4v4G9eOrw1v09lEKHB9WtiBVhhxKK1LnUjPEH3ifkOkgW7jFfoYgTdtB3XaXVgYnNPDFo PTBYsJy+wr89XfyHr2Ev7BB3Xaf7qICXdBF8MEVY8t/UFsesg4wFWOuzCfqxFmKEaPDZlTuR tfLAeVpslNfWCi5ybPlowLx6KJqOsI9R2a9o4qRXWGP7IwiMRAC3iiPyk9cknt8ee6EUIxI6 t847eFaVKI/6WcxhszI0R6Cj+N4y+1rHfkGWYWupCiHwj9DjILW9iEAncVgQmkNPpUsZECLT 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XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg== Message-ID: <660515dd-eb8a-36cc-5fac-a7814bb3ef69@ozlabs.ru> Date: Wed, 13 Feb 2019 11:37:00 +1100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: <20190212171839.env4rnjwdjyips6z@ca-dmjordan1.us.oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 13/02/2019 04:18, Daniel Jordan wrote: > On Tue, Feb 12, 2019 at 04:50:11PM +0000, Christopher Lameter wrote: >> On Tue, 12 Feb 2019, Alexey Kardashevskiy wrote: >> >>> Now it is 3 independent accesses (actually 4 but the last one is >>> diagnostic) with no locking around them. Why do not we need a lock >>> anymore precisely? Thanks, >> >> Updating a regular counter is racy and requires a lock. It was converted >> to be an atomic which can be incremented without a race. > > Yes, though Alexey may have meant that the multiple reads of the atomic in > decrement_pinned_vm are racy. Yes, I meant this race, thanks for clarifying this. > It only matters when there's a bug that would > make the counter go negative, but it's there. > > And FWIW the debug print in try_increment_pinned_vm is also racy. > > This fixes all that. It doesn't try to correct the negative pinned_vm as the > old code did because it's already a bug and adjusting the value by the negative > amount seems to do nothing but make debugging harder. > > If it's ok, I'll respin the whole series this way (another point for common > helper) This looks good, thanks for fixing this. > > diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c > index f47e020dc5e4..b79257304de6 100644 > --- a/drivers/vfio/vfio_iommu_spapr_tce.c > +++ b/drivers/vfio/vfio_iommu_spapr_tce.c > @@ -53,25 +53,24 @@ static long try_increment_pinned_vm(struct mm_struct *mm, long npages) > atomic64_sub(npages, &mm->pinned_vm); > } > > - pr_debug("[%d] RLIMIT_MEMLOCK +%ld %ld/%lu%s\n", current->pid, > - npages << PAGE_SHIFT, > - atomic64_read(&mm->pinned_vm) << PAGE_SHIFT, > - rlimit(RLIMIT_MEMLOCK), ret ? " - exceeded" : ""); > + pr_debug("[%d] RLIMIT_MEMLOCK +%ld %lld/%lu%s\n", current->pid, > + npages << PAGE_SHIFT, pinned << PAGE_SHIFT, > + lock_limit, ret ? " - exceeded" : ""); > > return ret; > } > > static void decrement_pinned_vm(struct mm_struct *mm, long npages) > { > + s64 pinned; > + > if (!mm || !npages) > return; > > - if (WARN_ON_ONCE(npages > atomic64_read(&mm->pinned_vm))) > - npages = atomic64_read(&mm->pinned_vm); > - atomic64_sub(npages, &mm->pinned_vm); > - pr_debug("[%d] RLIMIT_MEMLOCK -%ld %ld/%lu\n", current->pid, > - npages << PAGE_SHIFT, > - atomic64_read(&mm->pinned_vm) << PAGE_SHIFT, > + pinned = atomic64_sub_return(npages, &mm->pinned_vm); > + WARN_ON_ONCE(pinned < 0); > + pr_debug("[%d] RLIMIT_MEMLOCK -%ld %lld/%lu\n", current->pid, > + npages << PAGE_SHIFT, pinned << PAGE_SHIFT, > rlimit(RLIMIT_MEMLOCK)); > } > > -- Alexey