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Mon, 1 Sep 2025 09:14:51 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 493KAwtktWhvagAAD6G6ig (envelope-from ); Mon, 01 Sep 2025 09:14:51 +0000 Message-ID: Date: Mon, 1 Sep 2025 11:14:50 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] mm: slub: avoid wake up kswapd in set_track_prepare Content-Language: en-US To: yangshiguang Cc: David Rientjes , harry.yoo@oracle.com, akpm@linux-foundation.org, cl@gentwo.org, roman.gushchin@linux.dev, glittao@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, yangshiguang , stable@vger.kernel.org References: <20250830020946.1767573-1-yangshiguang1011@163.com> <7f30ddd1-c6f7-4b2b-a2b9-875844092e28@suse.cz> <11922bd5.7fae.1990464d9c8.Coremail.yangshiguang1011@163.com> <623a8fd2.8b7b.1990481f065.Coremail.yangshiguang1011@163.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Level: X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; FREEMAIL_TO(0.00)[163.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_SEVEN(0.00)[11]; FREEMAIL_ENVRCPT(0.00)[163.com,gmail.com]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[google.com,oracle.com,linux-foundation.org,gentwo.org,linux.dev,gmail.com,kvack.org,vger.kernel.org,xiaomi.com]; MID_RHS_MATCH_FROM(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; URIBL_BLOCKED(0.00)[suse.cz:email,suse.cz:mid,xiaomi.com:email]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Flag: NO X-Spam-Score: -4.30 On 9/1/25 11:00, yangshiguang wrote: > > > At 2025-09-01 16:46:13, "Vlastimil Babka" wrote: >>On 9/1/25 10:29, yangshiguang wrote: >>> >>> >>> At 2025-09-01 16:15:04, "Vlastimil Babka" wrote: >>>>On 9/1/25 09:50, David Rientjes wrote: >>>>> On Sat, 30 Aug 2025, yangshiguang1011@163.com wrote: >>>>> >>>>>> From: yangshiguang >>>>>> >>>>>> From: yangshiguang >>>>>> >>>>> >>>>> Duplicate lines. >>>>> >>>>>> set_track_prepare() can incur lock recursion. >>>>>> The issue is that it is called from hrtimer_start_range_ns >>>>>> holding the per_cpu(hrtimer_bases)[n].lock, but when enabled >>>>>> CONFIG_DEBUG_OBJECTS_TIMERS, may wake up kswapd in set_track_prepare, >>>>>> and try to hold the per_cpu(hrtimer_bases)[n].lock. >>>>>> >>>>>> Avoid deadlock caused by implicitly waking up kswapd by >>>>>> passing in allocation flags. And the slab caller context has >>>>>> preemption disabled, so __GFP_KSWAPD_RECLAIM must not appear in gfp_flags. >>>>>> >>>>> >>>>> This mentions __GFP_KSWAPD_RECLAIM, but the patch actually masks off >>>>> __GFP_DIRECT_RECLAIM which would be a heavierweight operation. Disabling >>>>> direct reclaim does not necessarily imply that kswapd will be disabled as >>>>> well. >>>> >>>>Yeah I think the changelog should say __GFP_DIRECT_RECLAIM. >>>> >>>>> Are you meaning to clear __GFP_RECLAIM in set_track_prepare()? >>>> >>>>No because if the context context (e.g. the hrtimers) can't support >>>>__GFP_KSWAPD_RECLAIM it won't have it in gfp_flags and we now pass them to >>> >>>>set_track_prepare() so it already won't be there. >>> >>> >>> Sry. Should be __GFP_DIRECT_RECLAIM. I will resend the patch. >> >>I have adjusted it locally already. Also moved the masking of >>__GFP_DIRECT_RECLAIM to ___slab_alloc itself as that's where >>the preemption is disabled so it's more obvious. >> >>Does the result look good to you? > > This looks good. > Currently only ___slab_alloc disables preemption context calls to set_track. > In the future, not all callers will disable preemption. Great, added to slab/for-next-fixes. Thanks!