From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 17A4424A07C; Tue, 20 May 2025 14:12:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747750375; cv=none; b=Qgl0mTyCpBLKB7KA2nufNnXZY9M3MT7BG9r9PckWfrqBPlnjTkctoT64SHaUu++DilrmMKlvL5tZQOf4v6Zn03LFRL4nON7NY3k31g8SCffsQbRez2erB9DuML3KCRiwG50sRholMdUIGehx5heSvsjAFRR4HxubIn9RGb+1Oq0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747750375; c=relaxed/simple; bh=7E8Lw9EqEXiWSITftJ9tgJas7bWqsNrWYeezIKnR4mk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=W6+rlnJX+ZjHFc4Ig9E6me15ezmt0fAy56seWux3JrpNM7KhKx3lfa72FYbPPrVYg1AC1Zva53aD3b9Hj8Gn1OQQTL+AWB5/GYYEVIPP629XgBZQ+n+UoQp/02UouYstkkUmzy1Jnx+qbAR2lsPQsg0TRNjsROJGCnEpRsjP8Uo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=tFakrdBY; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="tFakrdBY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 94FBAC4CEE9; Tue, 20 May 2025 14:12:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1747750375; bh=7E8Lw9EqEXiWSITftJ9tgJas7bWqsNrWYeezIKnR4mk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tFakrdBYfktAZlJlHXcpTvEqRFAeQgEjvVDiFt4D8qBcGO9yecX608XMCSppbRWKb rdZwmSo4bTtao4/sJNCn2dA8qQkNojohSsQGvM4ff9CdPNWP8Zu6h7viQrcEwJ1WwB bKxXSHh+eb3VBWRmRy/8yjoPunsUGgbq7c4mF5h4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Kirill A. Shutemov" , Borislav Petkov , Thomas Gleixner , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Andrew Morton Subject: [PATCH 6.12 131/143] mm/page_alloc: fix race condition in unaccepted memory handling Date: Tue, 20 May 2025 15:51:26 +0200 Message-ID: <20250520125815.169021780@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250520125810.036375422@linuxfoundation.org> References: <20250520125810.036375422@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kirill A. Shutemov commit fefc075182275057ce607effaa3daa9e6e3bdc73 upstream. The page allocator tracks the number of zones that have unaccepted memory using static_branch_enc/dec() and uses that static branch in hot paths to determine if it needs to deal with unaccepted memory. Borislav and Thomas pointed out that the tracking is racy: operations on static_branch are not serialized against adding/removing unaccepted pages to/from the zone. Sanity checks inside static_branch machinery detects it: WARNING: CPU: 0 PID: 10 at kernel/jump_label.c:276 __static_key_slow_dec_cpuslocked+0x8e/0xa0 The comment around the WARN() explains the problem: /* * Warn about the '-1' case though; since that means a * decrement is concurrent with a first (0->1) increment. IOW * people are trying to disable something that wasn't yet fully * enabled. This suggests an ordering problem on the user side. */ The effect of this static_branch optimization is only visible on microbenchmark. Instead of adding more complexity around it, remove it altogether. Link: https://lkml.kernel.org/r/20250506133207.1009676-1-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Fixes: dcdfdd40fa82 ("mm: Add support for unaccepted memory") Link: https://lore.kernel.org/all/20250506092445.GBaBnVXXyvnazly6iF@fat_crate.local Reported-by: Borislav Petkov Tested-by: Borislav Petkov (AMD) Reported-by: Thomas Gleixner Cc: Vlastimil Babka Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Brendan Jackman Cc: Johannes Weiner Cc: [6.5+] Signed-off-by: Andrew Morton Signed-off-by: Kirill A. Shutemov Signed-off-by: Greg Kroah-Hartman --- mm/page_alloc.c | 23 ----------------------- 1 file changed, 23 deletions(-) --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -7041,9 +7041,6 @@ bool has_managed_dma(void) #ifdef CONFIG_UNACCEPTED_MEMORY -/* Counts number of zones with unaccepted pages. */ -static DEFINE_STATIC_KEY_FALSE(zones_with_unaccepted_pages); - static bool lazy_accept = true; static int __init accept_memory_parse(char *p) @@ -7070,11 +7067,7 @@ static bool page_contains_unaccepted(str static void __accept_page(struct zone *zone, unsigned long *flags, struct page *page) { - bool last; - list_del(&page->lru); - last = list_empty(&zone->unaccepted_pages); - account_freepages(zone, -MAX_ORDER_NR_PAGES, MIGRATE_MOVABLE); __mod_zone_page_state(zone, NR_UNACCEPTED, -MAX_ORDER_NR_PAGES); __ClearPageUnaccepted(page); @@ -7083,9 +7076,6 @@ static void __accept_page(struct zone *z accept_memory(page_to_phys(page), PAGE_SIZE << MAX_PAGE_ORDER); __free_pages_ok(page, MAX_PAGE_ORDER, FPI_TO_TAIL); - - if (last) - static_branch_dec(&zones_with_unaccepted_pages); } void accept_page(struct page *page) @@ -7122,19 +7112,11 @@ static bool try_to_accept_memory_one(str return true; } -static inline bool has_unaccepted_memory(void) -{ - return static_branch_unlikely(&zones_with_unaccepted_pages); -} - static bool cond_accept_memory(struct zone *zone, unsigned int order) { long to_accept, wmark; bool ret = false; - if (!has_unaccepted_memory()) - return false; - if (list_empty(&zone->unaccepted_pages)) return false; @@ -7168,22 +7150,17 @@ static bool __free_unaccepted(struct pag { struct zone *zone = page_zone(page); unsigned long flags; - bool first = false; if (!lazy_accept) return false; spin_lock_irqsave(&zone->lock, flags); - first = list_empty(&zone->unaccepted_pages); list_add_tail(&page->lru, &zone->unaccepted_pages); account_freepages(zone, MAX_ORDER_NR_PAGES, MIGRATE_MOVABLE); __mod_zone_page_state(zone, NR_UNACCEPTED, MAX_ORDER_NR_PAGES); __SetPageUnaccepted(page); spin_unlock_irqrestore(&zone->lock, flags); - if (first) - static_branch_inc(&zones_with_unaccepted_pages); - return true; }