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Mon, 27 Apr 2026 07:49:09 +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 UaCCHPUU72nrbAAAD6G6ig (envelope-from ); Mon, 27 Apr 2026 07:49:09 +0000 Date: Mon, 27 Apr 2026 09:49:03 +0200 From: Oscar Salvador To: Muchun Song Cc: David Hildenbrand , Andrew Morton , Greg Kroah-Hartman , "Rafael J. Wysocki" , Danilo Krummrich , muchun.song@linux.dev, Ying Huang , Dan Williams , Vishal Verma , Miaohe Lin , Naoya Horiguchi , linux-mm@kvack.org, linux-cxl@vger.kernel.org, driver-core@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/2] mm/memory_hotplug: fix memory block reference leak on remove Message-ID: References: <20260426144447.817722-1-songmuchun@bytedance.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260426144447.817722-1-songmuchun@bytedance.com> X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; MIME_TRACE(0.00)[0:+]; TAGGED_RCPT(0.00)[]; RCPT_COUNT_TWELVE(0.00)[17]; RCVD_TLS_ALL(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[kernel.org,linux-foundation.org,linuxfoundation.org,linux.dev,gmail.com,intel.com,huawei.com,kvack.org,vger.kernel.org,lists.linux.dev]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; URIBL_BLOCKED(0.00)[imap1.dmz-prg2.suse.org:helo,bytedance.com:email,suse.de:email,localhost.localdomain:mid]; DBL_BLOCKED_OPENRESOLVER(0.00)[localhost.localdomain:mid,imap1.dmz-prg2.suse.org:helo,bytedance.com:email,suse.de:email] X-Spam-Flag: NO X-Spam-Score: -2.80 X-Spam-Level: On Sun, Apr 26, 2026 at 10:44:46PM +0800, Muchun Song wrote: > remove_memory_blocks_and_altmaps() looks up each memory block with > find_memory_block(), which acquires a reference to the memory block > device. > > That reference is never dropped on this path, resulting in a leaked > device reference when removing memory blocks and their altmaps. Drop > the reference after retrieving mem->altmap and clearing mem->altmap, > before removing the memory block device. > > Fixes: 6b8f0798b85a ("mm/memory_hotplug: split memmap_on_memory requests across memblocks") > Cc: stable@vger.kernel.org > Signed-off-by: Muchun Song The change looks good but some comments below: Acked-by: Oscar Salvador The outcome of leaking the reference is that the final call to put_device() in device_unregister() leaves the memory block device linked in the system under /sys/ ? (besides not deleting the struct I guess) > --- > mm/memory_hotplug.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 2a943ec57c85..4426abb05655 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1422,6 +1422,7 @@ static void remove_memory_blocks_and_altmaps(u64 start, u64 size) > > altmap = mem->altmap; > mem->altmap = NULL; > + put_device(&mem->dev); 1) Six months from now we might not remember why we need to call put_device() here. I would put a comment like remove_memory_block has: "/* drop the ref. we got via find_memory_block() */" or something like that. 2) I kind of dislike having an internal put_device() lingering here in memory-hotplug code, it feels like it does not really belong here. Ideally we should have a high-level function in drivers/base/memory.c that calls put_device itself. Something like "put_memblock_dev", dunno, names are hard. -- Oscar Salvador SUSE Labs