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 506073D524D; Wed, 21 Jan 2026 18:36:07 +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=1769020567; cv=none; b=MjSR8r8ovpX2hulK+ioxo/wxFsbxvdjBKTOaAEdyr2edqslJKjOGlMMF9HIyIogupDDMXyw5/WBTlkNPjv4uv+LbdsAaiue3XCW/61+HnLamtDryQaL6ihqQwAUE+iiWjSmWRpSEK90hqx2K7xnO+bW/fzOg8PgPy/2HmmX2PVs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769020567; c=relaxed/simple; bh=HFZmG4+KiQ3uQylwo7WuuBRpoUZdLGpfliVYZ9XxZMo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GRIrdGInYgFYEKMu40qf78d5P0WJpKSl36w4o/HA3/s3AjyJYYxEvluDvL2q2fuFBR8tXn796Q6Yj6kKL+ZU/6Rww+pHmcoxfjHR9QknXzs2bPtxgqKYmPLwargL98YXJQfSy0br/r5aiFRtgJ8atJm6fbsyA9UtMgEwrxjb7l8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Pch96cDj; 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="Pch96cDj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 70A33C4CEF1; Wed, 21 Jan 2026 18:36:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1769020567; bh=HFZmG4+KiQ3uQylwo7WuuBRpoUZdLGpfliVYZ9XxZMo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Pch96cDjutAu84i0r9unEe6O0deohwDVsyrKWkwHWM6zhjikbgQNCdj/kjcYsucbw MvNW45yRY4A0kw+vf/itgEk8n8D7V7O/yPiy45RXB+wuZoTTfBpT/8tlQzQlIzZoqn c1KAel4PTzIH5dteP/v2QBuiukE+7Lu96g35liO0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Vlastimil Babka , kernel test robot , Mel Gorman , Brendan Jackman , Johannes Weiner , Michal Hocko , Sebastian Andrzej Siewior , Steven Rostedt , Suren Baghdasaryan , Zi Yan , Andrew Morton , Sasha Levin , Matthew Wilcox Subject: [PATCH 6.18 196/198] mm/page_alloc: prevent pcp corruption with SMP=n Date: Wed, 21 Jan 2026 19:17:04 +0100 Message-ID: <20260121181425.613134816@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260121181418.537774329@linuxfoundation.org> References: <20260121181418.537774329@linuxfoundation.org> User-Agent: quilt/0.69 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 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Vlastimil Babka commit 038a102535eb49e10e93eafac54352fcc5d78847 upstream. The kernel test robot has reported: BUG: spinlock trylock failure on UP on CPU#0, kcompactd0/28 lock: 0xffff888807e35ef0, .magic: dead4ead, .owner: kcompactd0/28, .owner_cpu: 0 CPU: 0 UID: 0 PID: 28 Comm: kcompactd0 Not tainted 6.18.0-rc5-00127-ga06157804399 #1 PREEMPT 8cc09ef94dcec767faa911515ce9e609c45db470 Call Trace: __dump_stack (lib/dump_stack.c:95) dump_stack_lvl (lib/dump_stack.c:123) dump_stack (lib/dump_stack.c:130) spin_dump (kernel/locking/spinlock_debug.c:71) do_raw_spin_trylock (kernel/locking/spinlock_debug.c:?) _raw_spin_trylock (include/linux/spinlock_api_smp.h:89 kernel/locking/spinlock.c:138) __free_frozen_pages (mm/page_alloc.c:2973) ___free_pages (mm/page_alloc.c:5295) __free_pages (mm/page_alloc.c:5334) tlb_remove_table_rcu (include/linux/mm.h:? include/linux/mm.h:3122 include/asm-generic/tlb.h:220 mm/mmu_gather.c:227 mm/mmu_gather.c:290) ? __cfi_tlb_remove_table_rcu (mm/mmu_gather.c:289) ? rcu_core (kernel/rcu/tree.c:?) rcu_core (include/linux/rcupdate.h:341 kernel/rcu/tree.c:2607 kernel/rcu/tree.c:2861) rcu_core_si (kernel/rcu/tree.c:2879) handle_softirqs (arch/x86/include/asm/jump_label.h:36 include/trace/events/irq.h:142 kernel/softirq.c:623) __irq_exit_rcu (arch/x86/include/asm/jump_label.h:36 kernel/softirq.c:725) irq_exit_rcu (kernel/softirq.c:741) sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1052) RIP: 0010:_raw_spin_unlock_irqrestore (arch/x86/include/asm/preempt.h:95 include/linux/spinlock_api_smp.h:152 kernel/locking/spinlock.c:194) free_pcppages_bulk (mm/page_alloc.c:1494) drain_pages_zone (include/linux/spinlock.h:391 mm/page_alloc.c:2632) __drain_all_pages (mm/page_alloc.c:2731) drain_all_pages (mm/page_alloc.c:2747) kcompactd (mm/compaction.c:3115) kthread (kernel/kthread.c:465) ? __cfi_kcompactd (mm/compaction.c:3166) ? __cfi_kthread (kernel/kthread.c:412) ret_from_fork (arch/x86/kernel/process.c:164) ? __cfi_kthread (kernel/kthread.c:412) ret_from_fork_asm (arch/x86/entry/entry_64.S:255) Matthew has analyzed the report and identified that in drain_page_zone() we are in a section protected by spin_lock(&pcp->lock) and then get an interrupt that attempts spin_trylock() on the same lock. The code is designed to work this way without disabling IRQs and occasionally fail the trylock with a fallback. However, the SMP=n spinlock implementation assumes spin_trylock() will always succeed, and thus it's normally a no-op. Here the enabled lock debugging catches the problem, but otherwise it could cause a corruption of the pcp structure. The problem has been introduced by commit 574907741599 ("mm/page_alloc: leave IRQs enabled for per-cpu page allocations"). The pcp locking scheme recognizes the need for disabling IRQs to prevent nesting spin_trylock() sections on SMP=n, but the need to prevent the nesting in spin_lock() has not been recognized. Fix it by introducing local wrappers that change the spin_lock() to spin_lock_iqsave() with SMP=n and use them in all places that do spin_lock(&pcp->lock). [vbabka@suse.cz: add pcp_ prefix to the spin_lock_irqsave wrappers, per Steven] Link: https://lkml.kernel.org/r/20260105-fix-pcp-up-v1-1-5579662d2071@suse.cz Fixes: 574907741599 ("mm/page_alloc: leave IRQs enabled for per-cpu page allocations") Signed-off-by: Vlastimil Babka Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202512101320.e2f2dd6f-lkp@intel.com Analyzed-by: Matthew Wilcox Link: https://lore.kernel.org/all/aUW05pyc9nZkvY-1@casper.infradead.org/ Acked-by: Mel Gorman Cc: Brendan Jackman Cc: Johannes Weiner Cc: Michal Hocko Cc: Sebastian Andrzej Siewior Cc: Steven Rostedt Cc: Suren Baghdasaryan Cc: Zi Yan Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- mm/page_alloc.c | 47 +++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 39 insertions(+), 8 deletions(-) --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -166,6 +166,33 @@ static DEFINE_MUTEX(pcp_batch_high_lock) #define pcp_spin_unlock(ptr) \ pcpu_spin_unlock(lock, ptr) +/* + * With the UP spinlock implementation, when we spin_lock(&pcp->lock) (for i.e. + * a potentially remote cpu drain) and get interrupted by an operation that + * attempts pcp_spin_trylock(), we can't rely on the trylock failure due to UP + * spinlock assumptions making the trylock a no-op. So we have to turn that + * spin_lock() to a spin_lock_irqsave(). This works because on UP there are no + * remote cpu's so we can only be locking the only existing local one. + */ +#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT) +static inline void __flags_noop(unsigned long *flags) { } +#define pcp_spin_lock_maybe_irqsave(ptr, flags) \ +({ \ + __flags_noop(&(flags)); \ + spin_lock(&(ptr)->lock); \ +}) +#define pcp_spin_unlock_maybe_irqrestore(ptr, flags) \ +({ \ + spin_unlock(&(ptr)->lock); \ + __flags_noop(&(flags)); \ +}) +#else +#define pcp_spin_lock_maybe_irqsave(ptr, flags) \ + spin_lock_irqsave(&(ptr)->lock, flags) +#define pcp_spin_unlock_maybe_irqrestore(ptr, flags) \ + spin_unlock_irqrestore(&(ptr)->lock, flags) +#endif + #ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID DEFINE_PER_CPU(int, numa_node); EXPORT_PER_CPU_SYMBOL(numa_node); @@ -2555,6 +2582,7 @@ static int rmqueue_bulk(struct zone *zon bool decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp) { int high_min, to_drain, to_drain_batched, batch; + unsigned long UP_flags; bool todo = false; high_min = READ_ONCE(pcp->high_min); @@ -2574,9 +2602,9 @@ bool decay_pcp_high(struct zone *zone, s to_drain = pcp->count - pcp->high; while (to_drain > 0) { to_drain_batched = min(to_drain, batch); - spin_lock(&pcp->lock); + pcp_spin_lock_maybe_irqsave(pcp, UP_flags); free_pcppages_bulk(zone, to_drain_batched, pcp, 0); - spin_unlock(&pcp->lock); + pcp_spin_unlock_maybe_irqrestore(pcp, UP_flags); todo = true; to_drain -= to_drain_batched; @@ -2593,14 +2621,15 @@ bool decay_pcp_high(struct zone *zone, s */ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp) { + unsigned long UP_flags; int to_drain, batch; batch = READ_ONCE(pcp->batch); to_drain = min(pcp->count, batch); if (to_drain > 0) { - spin_lock(&pcp->lock); + pcp_spin_lock_maybe_irqsave(pcp, UP_flags); free_pcppages_bulk(zone, to_drain, pcp, 0); - spin_unlock(&pcp->lock); + pcp_spin_unlock_maybe_irqrestore(pcp, UP_flags); } } #endif @@ -2611,10 +2640,11 @@ void drain_zone_pages(struct zone *zone, static void drain_pages_zone(unsigned int cpu, struct zone *zone) { struct per_cpu_pages *pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu); + unsigned long UP_flags; int count; do { - spin_lock(&pcp->lock); + pcp_spin_lock_maybe_irqsave(pcp, UP_flags); count = pcp->count; if (count) { int to_drain = min(count, @@ -2623,7 +2653,7 @@ static void drain_pages_zone(unsigned in free_pcppages_bulk(zone, to_drain, pcp, 0); count -= to_drain; } - spin_unlock(&pcp->lock); + pcp_spin_unlock_maybe_irqrestore(pcp, UP_flags); } while (count); } @@ -6081,6 +6111,7 @@ static void zone_pcp_update_cacheinfo(st { struct per_cpu_pages *pcp; struct cpu_cacheinfo *cci; + unsigned long UP_flags; pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu); cci = get_cpu_cacheinfo(cpu); @@ -6091,12 +6122,12 @@ static void zone_pcp_update_cacheinfo(st * This can reduce zone lock contention without hurting * cache-hot pages sharing. */ - spin_lock(&pcp->lock); + pcp_spin_lock_maybe_irqsave(pcp, UP_flags); if ((cci->per_cpu_data_slice_size >> PAGE_SHIFT) > 3 * pcp->batch) pcp->flags |= PCPF_FREE_HIGH_BATCH; else pcp->flags &= ~PCPF_FREE_HIGH_BATCH; - spin_unlock(&pcp->lock); + pcp_spin_unlock_maybe_irqrestore(pcp, UP_flags); } void setup_pcp_cacheinfo(unsigned int cpu)