From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 2F72D4137A1; Fri, 25 Sep 2026 05:25:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790313934; cv=none; b=hSo2g55cr6CqXWQW7ZOVipybyS2KQyktM+Lqebmifnvb1Xer62zskfmE1mmzZaMXsT1j7Ns/JElRaeX6hbnb6dVOOQEucQyimDtDLIrr+AQhWXpAsuAMesJ06dofDBkc6j4uNqW8Z8/cqKBuCBtVPjQBsGX74kxmjT3imb43vFQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790313934; c=relaxed/simple; bh=8yIYAloJhsj6APeeyij6SLEY+Bleic8cLRqnrJJAFoE=; h=Date:To:From:Subject:Message-Id; b=VBYdlo3KT2VEK9ftFr779+nq6q2DZwPpiHlIO1DT6bmlmmtNw25ZoUaH4pz+7hTY4xjJOW7k9C0hXIwVjrIz7HYEQb+9tJUAVjCvR5dNrdiLphCZnWNaj4X/pLPjGvSU3acFAZTTED6vdOUHmQGsdHe7lsEUg+UPbRK3v3xRhRM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=WBDzMMmg; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="WBDzMMmg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8A7961F000FF; Fri, 25 Sep 2026 05:25:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1790313932; bh=bsP5ecIt1PtAv8g9LwbVVlaL4CBxqhj5muOKFhuu83Q=; h=Date:To:From:Subject; b=WBDzMMmgYfGKBsIxjSnsiKDVbjaGmqpArJaAYDf0YgRQ6ON1jEnsbtuHeSC6R5UtH Kwu/ixKqtzGx6pgLc3evVvBUBb2TCIBEQh06mPEERqNZC/OozKk1wZGq7KVedj0gX2 SQ9Hue20q0cRrvalSH0vTqS7puSdJDMyxdZZrST8= Date: Thu, 24 Sep 2026 22:25:32 -0700 To: mm-commits@vger.kernel.org,vishal.moola@gmail.com,vbabka@kernel.org,surenb@google.com,stable@vger.kernel.org,rppt@kernel.org,rostedt@goodmis.org,mingo@kernel.org,mhocko@suse.com,ljs@kernel.org,liam@infradead.org,jgg@ziepe.ca,david@kernel.org,dave.hansen@linux.intel.com,baolu.lu@linux.intel.com,akpm@linux-foundation.org,mikhail.v.gavrilov@gmail.com From: Andrew Morton Subject: + mm-dont-schedule-deferred-kernel-page-table-freeing-while-booting.patch added to mm-hotfixes-unstable branch Message-Id: <20260925052532.8A7961F000FF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: don't schedule deferred kernel page table freeing while booting has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-dont-schedule-deferred-kernel-page-table-freeing-while-booting.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-dont-schedule-deferred-kernel-page-table-freeing-while-booting.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Mikhail Gavrilov Subject: mm: don't schedule deferred kernel page table freeing while booting Date: Fri, 25 Sep 2026 10:06:47 +0500 Booting with a boot-time function tracer and a filter, for example ftrace=function ftrace_filter=pud_free_pmd_page panics on 7.3-rc4 as soon as the tracer starts: [ 23.531178] Starting tracer 'function' [ 23.675800] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000038: 0000 [#1] SMP KASAN NOPTI [ 23.819917] KASAN: null-ptr-deref in range [0x00000000000001c0-0x00000000000001c7] [ 23.964025] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 7.3.0-rc4-fe2ec83746e5-with-fixes-v2+ #195 PREEMPT(undef) [ 24.252248] RIP: 0010:__queue_work+0xab/0xf00 [ 25.981629] Call Trace: [ 26.125727] [ 26.413912] ? pagetable_free_kernel+0x20/0x120 [ 26.990283] queue_work_on+0x97/0xf0 [ 27.134382] __cpa_collapse_large_pages+0x501/0x6f0 [ 27.566662] cpa_flush+0x394/0x620 [ 27.998953] change_page_attr_set_clr+0x321/0x4a0 [ 29.151729] set_memory_rox+0xa2/0xf0 [ 29.584018] create_trampoline+0x431/0x6f0 ... [ 44.343347] Kernel panic - not syncing: Attempted to kill the idle task! The boot-time tracer is started from early_trace_init(), which runs before workqueue_init_early(). Making its trampoline read-only splits a large page, and CPA collapses it again right away. The split table has been a kernel page table since commit 9e4a3ec3411b ("x86/mm/pat: Allocate split page tables as kernel page tables"), so the collapse frees it through pagetable_free_kernel(), which queues work on system_percpu_wq - still NULL at that point. That commit is correct in itself; it only lets CPA reach pagetable_free_kernel() before the workqueue that function relies on exists. Keep putting the table on the list, but don't schedule the work while the system is still booting. A core_initcall schedules it once to free whatever was queued by then. Link: https://lore.kernel.org/20260925050647.86913-1-mikhail.v.gavrilov@gmail.com Link: https://lore.kernel.org/20260924064321.23787-1-mikhail.v.gavrilov@gmail.com Fixes: 9e4a3ec3411b ("x86/mm/pat: Allocate split page tables as kernel page tables") Signed-off-by: Mikhail Gavrilov Signed-off-by: Andrew Morton Suggested-by: David Hildenbrand (Arm) Suggested-by: Lorenzo Stoakes (ARM) Reviewed-by: Andrew Morton Cc: Dave Hansen Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Vishal Moola (Oracle) Cc: Ingo Molnar Cc: Lu Baolu Cc: Jason Gunthorpe Cc: Steven Rostedt Cc: --- mm/pgtable-generic.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) --- a/mm/pgtable-generic.c~mm-dont-schedule-deferred-kernel-page-table-freeing-while-booting +++ a/mm/pgtable-generic.c @@ -438,12 +438,30 @@ static void kernel_pgtable_work_func(str __pagetable_free(pt); } +static void schedule_kernel_pgtable_free(void) +{ + schedule_work(&kernel_pgtable_work.work); +} + void pagetable_free_kernel(struct ptdesc *pt) { spin_lock(&kernel_pgtable_work.lock); list_add(&pt->pt_list, &kernel_pgtable_work.list); spin_unlock(&kernel_pgtable_work.lock); - schedule_work(&kernel_pgtable_work.work); + /* + * The workqueue may not exist yet while the system is booting. + * kernel_pgtable_drain_early() schedules the work once it does. + */ + if (system_state != SYSTEM_BOOTING) + schedule_kernel_pgtable_free(); +} + +static int __init kernel_pgtable_drain_early(void) +{ + /* Free the kernel page tables queued while booting. */ + schedule_kernel_pgtable_free(); + return 0; } +core_initcall(kernel_pgtable_drain_early); #endif _ Patches currently in -mm which might be from mikhail.v.gavrilov@gmail.com are mm-dont-schedule-deferred-kernel-page-table-freeing-while-booting.patch