From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (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 7A2293A5444 for ; Thu, 30 Apr 2026 20:22:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=96.67.55.147 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777580577; cv=none; b=Hx8oOP2hFIzBu4I7BFgkaXvWSreGi6JuktAFuToEEipGyGTT6gqTv1XiLlCb5HpMrlnMD2W7coxWB05Gh/dpeXiAvT9JtJHoNlGZbxCVAgq/2oAoi7zUCOahjgldT26qjY88o9VIq46dmgfrRSuK0fUvBqqe2l8KgY+nFuPMSnI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777580577; c=relaxed/simple; bh=w2cJxepI0NOh3zxR8VnPTqpRdjSGRj+L20DO79oGclE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OwvV8sWVUNiYLVf0F6w+a9VqDP+G4BOa/7EzndUqytJ6gU70d8QLXniJIXbxHZZQ4ktTNHBnPEe/lUO0nFQRA1wBHrV801K7+lo0SluecZGl9ItvudkGvskug3Hq9QfANdrJuEYefniMFhZyy18one3GG+3a+eDRfJ6udFmTgUk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com; spf=pass smtp.mailfrom=surriel.com; dkim=pass (2048-bit key) header.d=surriel.com header.i=@surriel.com header.b=awZxtyZw; arc=none smtp.client-ip=96.67.55.147 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=surriel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=surriel.com header.i=@surriel.com header.b="awZxtyZw" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=surriel.com ; s=mail; h=Content-Transfer-Encoding:MIME-Version:References:In-Reply-To: Message-ID:Date:Subject:Cc:To:From:Sender:Reply-To:Content-Type:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=kt5GNjBeLABnBd/hL+1b6b1fMeRkP20n1Tblpb4QH04=; b=awZxtyZwecddB6EvRPOgcqqGvA IRcXu9Yscs0Joo/AXlv0RwllD4aKOn6TlWwsD/aTzEmiIoXbc7A7xCBtrOWj1BEMaBHN1NGM+/HPq bJJJ0pic+Vg4BF/wVt/hP5TIwMHmMxqQiWXA/mYA4v+jp11ld7aB2fPQlS8uh1rowrzXCFOov9xs+ hro+ThRizVBODDqPqs0LeLxC9Mg8YdGIZgdYALhYVtuev7iyUNJKqWTU7QW0jAxFeOCOXSgWe92ln lm2mkRVbijdou3SwLRLQRXiA5nTG0Iv5GHEjtB6Kg/txhs+X5n82zQYvRZraewN+P2umAec/UF5zn 3MFqto3Q==; Received: from fangorn.home.surriel.com ([10.0.13.7]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1wIXuC-000000001R0-45zn; Thu, 30 Apr 2026 16:22:40 -0400 From: Rik van Riel To: linux-kernel@vger.kernel.org Cc: kernel-team@meta.com, linux-mm@kvack.org, david@kernel.org, willy@infradead.org, surenb@google.com, hannes@cmpxchg.org, ljs@kernel.org, ziy@nvidia.com, usama.arif@linux.dev, Rik van Riel , Rik van Riel Subject: [RFC PATCH 23/45] mm: page_alloc: add CONFIG_DEBUG_VM sanity checks for SPB counters Date: Thu, 30 Apr 2026 16:20:52 -0400 Message-ID: <20260430202233.111010-24-riel@surriel.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260430202233.111010-1-riel@surriel.com> References: <20260430202233.111010-1-riel@surriel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Rik van Riel Add spb_debug_check() and call it after every site that mutates the per-superpageblock type counters (nr_free / nr_unmovable / nr_reclaimable / nr_movable). Each counter must be <= total_pageblocks; a violation indicates that a PB_has_ bit transition was missed by one of the allocation, free, claim, or evacuation paths and the counter has drifted out of sync with the bits. VM_WARN_ONCE keeps the production cost zero (CONFIG_DEBUG_VM only) while giving us a single place to catch counter drift early during stress testing instead of debugging it from a much later misaccounting symptom. Several real bugs in the SPB stack were caught by this check during development; keeping it permanently makes future churn safer. Signed-off-by: Rik van Riel Assisted-by: Claude:claude-opus-4.7 syzkaller --- mm/page_alloc.c | 46 +++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 41 insertions(+), 5 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 4f8105b89e47..9f4298fc2727 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -521,6 +521,32 @@ static inline int migratetype_to_has_bit(int migratetype) } } +#ifdef CONFIG_DEBUG_VM +static void spb_debug_check(struct superpageblock *sb, const char *caller) +{ + u16 total = sb->total_pageblocks; + + VM_WARN_ONCE(sb->nr_free > total, + "%s: nr_free %u > total %u (zone=%s sb=%lu)\n", + caller, sb->nr_free, total, sb->zone->name, + (unsigned long)(sb - sb->zone->superpageblocks)); + VM_WARN_ONCE(sb->nr_unmovable > total, + "%s: nr_unmovable %u > total %u (zone=%s sb=%lu)\n", + caller, sb->nr_unmovable, total, sb->zone->name, + (unsigned long)(sb - sb->zone->superpageblocks)); + VM_WARN_ONCE(sb->nr_reclaimable > total, + "%s: nr_reclaimable %u > total %u (zone=%s sb=%lu)\n", + caller, sb->nr_reclaimable, total, sb->zone->name, + (unsigned long)(sb - sb->zone->superpageblocks)); + VM_WARN_ONCE(sb->nr_movable > total, + "%s: nr_movable %u > total %u (zone=%s sb=%lu)\n", + caller, sb->nr_movable, total, sb->zone->name, + (unsigned long)(sb - sb->zone->superpageblocks)); +} +#else +static inline void spb_debug_check(struct superpageblock *sb, const char *caller) {} +#endif + /* * __spb_set_has_type - set PB_has_* and increment type counter * @@ -552,6 +578,7 @@ static void __spb_set_has_type(struct page *page, int migratetype) sb->nr_movable++; break; } + spb_debug_check(sb, "__spb_set_has_type"); } } @@ -589,6 +616,7 @@ static void __spb_clear_has_type(struct page *page, int migratetype) sb->nr_movable--; break; } + spb_debug_check(sb, "__spb_clear_has_type"); } } @@ -818,6 +846,7 @@ static void superpageblock_pb_now_free(struct page *page) return; sb->nr_free++; + spb_debug_check(sb, "pb_now_free"); spb_update_list(sb); } @@ -840,6 +869,7 @@ static void superpageblock_pb_now_used(struct page *page) if (sb->nr_free) sb->nr_free--; + spb_debug_check(sb, "pb_now_used"); spb_update_list(sb); } @@ -1305,7 +1335,9 @@ static inline void __add_to_free_list(struct page *page, struct zone *zone, struct free_area *area = pfn_sb_free_area(zone, pfn, order, &sb); int nr_pages = 1 << order; - VM_WARN_ONCE(get_pageblock_migratetype(page) != migratetype, + VM_WARN_ONCE(get_pageblock_migratetype(page) != migratetype && + !is_migrate_isolate(get_pageblock_migratetype(page)) && + !is_migrate_cma(get_pageblock_migratetype(page)), "page type is %d, passed migratetype is %d (nr=%d)\n", get_pageblock_migratetype(page), migratetype, nr_pages); @@ -1339,7 +1371,8 @@ static inline void move_to_free_list(struct page *page, struct zone *zone, int nr_pages = 1 << order; /* Free page moving can fail, so it happens before the type update */ - VM_WARN_ONCE(get_pageblock_migratetype(page) != old_mt, + VM_WARN_ONCE(get_pageblock_migratetype(page) != old_mt && + !is_migrate_cma(get_pageblock_migratetype(page)), "page type is %d, passed migratetype is %d (nr=%d)\n", get_pageblock_migratetype(page), old_mt, nr_pages); @@ -1364,7 +1397,9 @@ static inline void __del_page_from_free_list(struct page *page, struct zone *zon struct free_area *area = pfn_sb_free_area(zone, pfn, order, &sb); int nr_pages = 1 << order; - VM_WARN_ONCE(get_pageblock_migratetype(page) != migratetype, + VM_WARN_ONCE(get_pageblock_migratetype(page) != migratetype && + !is_migrate_isolate(get_pageblock_migratetype(page)) && + !is_migrate_cma(get_pageblock_migratetype(page)), "page type is %d, passed migratetype is %d (nr=%d)\n", get_pageblock_migratetype(page), migratetype, nr_pages); @@ -10529,11 +10564,12 @@ static int superpageblock_debugfs_show(struct seq_file *m, void *v) i, sb->start_pfn, sb->total_pageblocks); else - seq_printf(m, " sb[%lu] pfn=0x%lx: unmov=%u recl=%u mov=%u rsv=%u free=%u total=%u\n", + seq_printf(m, " sb[%lu] pfn=0x%lx: unmov=%u recl=%u mov=%u rsv=%u free=%u total=%u free_pages=%lu\n", i, sb->start_pfn, sb->nr_unmovable, sb->nr_reclaimable, sb->nr_movable, sb->nr_reserved, - sb->nr_free, sb->total_pageblocks); + sb->nr_free, sb->total_pageblocks, + sb->nr_free_pages); } } return 0; -- 2.52.0