From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay8-d.mail.gandi.net (relay8-d.mail.gandi.net [217.70.183.201]) (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 877968289A; Wed, 22 May 2024 11:22:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.70.183.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716376962; cv=none; b=BowvoyVYBTD7O3T5Vkcbi14LvQVQ9uRkX+yF4VCR/prWT5MeSj56L1AyhkAG9vfA01mC2/TmllHnXxPR6anEK84oBpNrF5D6z7UvYWTI1CPq5/Om52nNi5/wax89vG/qceo1SFEDbSb+W9OaDipeKyIUCWQhukfr3G2RNukcshU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716376962; c=relaxed/simple; bh=F+eLMP7vomG4vgGnf2QTGMnK4y1oDm374YCutBXL7wU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=mZStDywAVhFGYMF4ff7lXLFDjIOhRQEaYw9S3dUVJplgBPYajMu/K05U4HaCUDdrqPaf/MJ/enrA2wj44FJsPK7EwCUMvYmdfMCaBGHQqo7WJtfSFCzOyDKWHbPYDiLkt8ga7EC5V7RfDk1a1KClnFfBLOKOuTp7QRoK8213ths= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ghiti.fr; spf=pass smtp.mailfrom=ghiti.fr; arc=none smtp.client-ip=217.70.183.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ghiti.fr Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ghiti.fr Received: by mail.gandi.net (Postfix) with ESMTPSA id E86A61BF207; Wed, 22 May 2024 11:22:32 +0000 (UTC) Message-ID: Date: Wed, 22 May 2024 13:22:31 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] riscv: rewrite __kernel_map_pages() to fix sleeping in invalid context Content-Language: en-US To: Nam Cao , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org References: <1289ecba9606a19917bc12b6c27da8aa23e1e5ae.1715750938.git.namcao@linutronix.de> From: Alexandre Ghiti In-Reply-To: <1289ecba9606a19917bc12b6c27da8aa23e1e5ae.1715750938.git.namcao@linutronix.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-GND-Sasl: alex@ghiti.fr On 15/05/2024 07:50, Nam Cao wrote: > __kernel_map_pages() is a debug function which clears the valid bit in page > table entry for deallocated pages to detect illegal memory accesses to > freed pages. > > This function set/clear the valid bit using __set_memory(). __set_memory() > acquires init_mm's semaphore, and this operation may sleep. This is > problematic, because __kernel_map_pages() can be called in atomic context, > and thus is illegal to sleep. An example warning that this causes: > > BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:1578 > in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 2, name: kthreadd > preempt_count: 2, expected: 0 > CPU: 0 PID: 2 Comm: kthreadd Not tainted 6.9.0-g1d4c6d784ef6 #37 > Hardware name: riscv-virtio,qemu (DT) > Call Trace: > [] dump_backtrace+0x1c/0x24 > [] show_stack+0x2c/0x38 > [] dump_stack_lvl+0x5a/0x72 > [] dump_stack+0x14/0x1c > [] __might_resched+0x104/0x10e > [] __might_sleep+0x3e/0x62 > [] down_write+0x20/0x72 > [] __set_memory+0x82/0x2fa > [] __kernel_map_pages+0x5a/0xd4 > [] __alloc_pages_bulk+0x3b2/0x43a > [] __vmalloc_node_range+0x196/0x6ba > [] copy_process+0x72c/0x17ec > [] kernel_clone+0x60/0x2fe > [] kernel_thread+0x82/0xa0 > [] kthreadd+0x14a/0x1be > [] ret_from_fork+0xe/0x1c > > Rewrite this function with apply_to_existing_page_range(). It is fine to > not have any locking, because __kernel_map_pages() works with pages being > allocated/deallocated and those pages are not changed by anyone else in the > meantime. > > Fixes: 5fde3db5eb02 ("riscv: add ARCH_SUPPORTS_DEBUG_PAGEALLOC support") > Signed-off-by: Nam Cao > Cc: stable@vger.kernel.org > --- > arch/riscv/mm/pageattr.c | 28 ++++++++++++++++++++++------ > 1 file changed, 22 insertions(+), 6 deletions(-) > > diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c > index 410056a50aa9..271d01a5ba4d 100644 > --- a/arch/riscv/mm/pageattr.c > +++ b/arch/riscv/mm/pageattr.c > @@ -387,17 +387,33 @@ int set_direct_map_default_noflush(struct page *page) > } > > #ifdef CONFIG_DEBUG_PAGEALLOC > +static int debug_pagealloc_set_page(pte_t *pte, unsigned long addr, void *data) > +{ > + int enable = *(int *)data; > + > + unsigned long val = pte_val(ptep_get(pte)); > + > + if (enable) > + val |= _PAGE_PRESENT; > + else > + val &= ~_PAGE_PRESENT; > + > + set_pte(pte, __pte(val)); > + > + return 0; > +} > + > void __kernel_map_pages(struct page *page, int numpages, int enable) > { > if (!debug_pagealloc_enabled()) > return; > > - if (enable) > - __set_memory((unsigned long)page_address(page), numpages, > - __pgprot(_PAGE_PRESENT), __pgprot(0)); > - else > - __set_memory((unsigned long)page_address(page), numpages, > - __pgprot(0), __pgprot(_PAGE_PRESENT)); > + unsigned long start = (unsigned long)page_address(page); > + unsigned long size = PAGE_SIZE * numpages; > + > + apply_to_existing_page_range(&init_mm, start, size, debug_pagealloc_set_page, &enable); > + > + flush_tlb_kernel_range(start, start + size); > } > #endif > And you can add: Reviewed-by: Alexandre Ghiti Thanks! Alex