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t=1672172495; bh=+6SHzFYpleoqvJNUY3JPRsP/mA1tz9L+T/ymsSLaI2o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bPZ6lNF8ptkFi2U99dBpZSEU7g4kFpmvGsmLyQjob5pGFhV4HWsnFWRzb9f57SP3Q EbcyPhR2M0B+ot83g3NsUJ/SdicbClIVr5jF4+wS2Cjq2cUwSCk7MjYavFguN3avMX Rx0/irB+tis7chl140KdkWANCB4hPcyXz+oOmA2ZZP5IWetY45a46ufosYlRBb9Bap B1ZnxJDy9lHfTMbT88gJbHANzz3ovqKSeBbbrt2Tp9F+2s4UP/VkJgODJDhKg5vmk4 WuMSDmmICljb32mvizzZcyLHfb2IpABfVK+y9REFN+m5d7iDxrEXaH8/9SubdO5kQj 8cBmLDeU2SEFw== Date: Tue, 27 Dec 2022 13:21:32 -0700 From: Keith Busch To: Christoph Hellwig Cc: Keith Busch , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Matthew Wilcox , Tony Battersby , Kernel Team Subject: Re: [PATCHv2 09/11] dmapool: simplify freeing Message-ID: References: <20221216201625.2362737-1-kbusch@meta.com> <20221216201625.2362737-10-kbusch@meta.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A5E651C0015 X-Stat-Signature: fq9kd75etmsu91zrbds6b4nkgrff3isj X-Rspam-User: X-HE-Tag: 1672172498-638006 X-HE-Meta: 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 t59RMMyS migD7SY6JM/Daepw5FJKIBMchSA== 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 Fri, Dec 23, 2022 at 08:38:55AM -0800, Christoph Hellwig wrote: > > @@ -280,14 +268,14 @@ void dma_pool_destroy(struct dma_pool *pool) > > mutex_unlock(&pools_reg_lock); > > > > list_for_each_entry_safe(page, tmp, &pool->page_list, page_list) { > > + if (!is_page_busy(page)) > > + dma_free_coherent(pool->dev, pool->allocation, > > + page->vaddr, page->dma); > > + else > > dev_err(pool->dev, "%s %s, %p busy\n", __func__, > > pool->name, page->vaddr); > > + list_del(&page->page_list); > > + kfree(page); > > Hmm. The is_page_busy case is really a should not happen case. > What is the benefit of skipping the dma_free_coherent and leaking > memory here, vs letting KASAN and friends see the free and possibly > help with debugging? In other words, why is this not: > > WARN_ON_ONCE(is_page_busy(page)); > dma_free_coherent(pool->dev, pool->allocation, page->vaddr, > page->dma); > ... The memory is presumed to still be owned by the device in this case, so the kernel shouldn't free it. I don't think KASAN will be very helpful if the device corrupts memory. > > page->in_use--; > > *(int *)vaddr = page->offset; > > page->offset = offset; > > - /* > > - * Resist a temptation to do > > - * if (!is_page_busy(page)) pool_free_page(pool, page); > > - * Better have a few empty pages hang around. > > - */ > > This doesn't look related to the rest, or am I missing something? Oops, this was supposed to go with a later patch in this series that removed "is_page_busy()".