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 368F016F265; Thu, 27 Nov 2025 12:59:28 +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=1764248369; cv=none; b=XhzZk6v2BTXdsHEHc0bDfZ9JqZCIkOKY4bKWEcnbyhylrYsv35XXd4RD33BvDEMzV7RZjnVstOuNi3m+eCkJWVIC1GA7u+jt6D/EkQ0R2aydkmnWaO0cuRu5ZwptijqXjz4JHjaqfd33zHXysGk56QwaxiamLKMEyF+L+Z1xDaQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764248369; c=relaxed/simple; bh=9FAZ+a3Saa3K2w/qcM5YJymiW3fVjUChcc0PgFLP3kM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VyalhX2IrJJwMFbLBOfNcWq9DGTEDSw06d3z7s9fr4kJAZxnPQBOIX41RcDR2rU26eAl9PPlYK+NwWdEh0oFBn7JW0wNhPJkMoxEq7sHfXNQwDQI/0+VdaPrw2kIB9nYYW2Jl3Dfb2do920p8/Am0dan8P+PPImoXZF7VE4LrYw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fI4FSWoN; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fI4FSWoN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F21B8C4CEF8; Thu, 27 Nov 2025 12:59:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764248368; bh=9FAZ+a3Saa3K2w/qcM5YJymiW3fVjUChcc0PgFLP3kM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fI4FSWoNziNxUPbDB6JkgJO1Yjnf6Bti878Qij6lf/sDn7w/gHEsxCWtwUKbfzIC7 1qXgeeNkfSyJhRfPo/0VWdYXYX4XMehPWqREme+oOWuyDGHPw8cDGW7ToctKEVSehA ui5RCOiknFcesTzXJ2Ca6+7A1XjGiV6XEAGWE3VL9D8J+DKMcpJ1Z6B9X3diNElvPw qwN9QiVjiXoWMzyQg5SknYsw+Gd2nxZApTimNOLjRHI5fhnt7oOZWcydR97/QNxkz7 +PgzdNbs94jarrIsGJ+qTzv5SBvS+hsNRz7eC90oioecBC1ZZaQmSWaMBECtd/ovl+ GIp6SjbV/s45w== Date: Thu, 27 Nov 2025 12:59:22 +0000 From: Will Deacon To: Zizhi Wo Cc: jack@suse.com, brauner@kernel.org, hch@lst.de, akpm@linux-foundation.org, linux@armlinux.org.uk, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, wozizhi@huawei.com, yangerkun@huawei.com, wangkefeng.wang@huawei.com, pangliyuan1@huawei.com, xieyuanbin1@huawei.com Subject: Re: [Bug report] hash_name() may cross page boundary and trigger sleep in RCU context Message-ID: References: <20251126090505.3057219-1-wozizhi@huaweicloud.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251126090505.3057219-1-wozizhi@huaweicloud.com> On Wed, Nov 26, 2025 at 05:05:05PM +0800, Zizhi Wo wrote: > We're running into the following issue on an ARM32 platform with the linux > 5.10 kernel: > > [] (__dabt_svc) from [] (link_path_walk.part.7+0x108/0x45c) > [] (link_path_walk.part.7) from [] (path_openat+0xc4/0x10ec) > [] (path_openat) from [] (do_filp_open+0x9c/0x114) > [] (do_filp_open) from [] (do_sys_openat2+0x418/0x528) > [] (do_sys_openat2) from [] (do_sys_open+0x88/0xe4) > [] (do_sys_open) from [] (ret_fast_syscall+0x0/0x58) > ... > [] (unwind_backtrace) from [] (show_stack+0x20/0x24) > [] (show_stack) from [] (dump_stack+0xd8/0xf8) > [] (dump_stack) from [] (___might_sleep+0x19c/0x1e4) > [] (___might_sleep) from [] (do_page_fault+0x2f8/0x51c) > [] (do_page_fault) from [] (do_DataAbort+0x90/0x118) > [] (do_DataAbort) from [] (__dabt_svc+0x58/0x80) > ... > > During the execution of hash_name()->load_unaligned_zeropad(), a potential > memory access beyond the PAGE boundary may occur. For example, when the > filename length is near the PAGE_SIZE boundary. This triggers a page fault, > which leads to a call to do_page_fault()->mmap_read_trylock(). If we can't > acquire the lock, we have to fall back to the mmap_read_lock() path, which > calls might_sleep(). This breaks RCU semantics because path lookup occurs > under an RCU read-side critical section. In linux-mainline, arm/arm64 > do_page_fault() still has this problem: > > lock_mm_and_find_vma->get_mmap_lock_carefully->mmap_read_lock_killable. > > And before commit bfcfaa77bdf0 ("vfs: use 'unsigned long' accesses for > dcache name comparison and hashing"), hash_name accessed the name byte by > byte. > > To prevent load_unaligned_zeropad() from accessing beyond the valid memory > region, we would need to intercept such cases beforehand? But doing so > would require replicating the internal logic of load_unaligned_zeropad(), > including handling endianness and constructing the correct value manually. > Given that load_unaligned_zeropad() is used in many places across the > kernel, we currently haven't found a good solution to address this cleanly. > > What would be the recommended way to handle this situation? Would > appreciate any feedback and guidance from the community. Thanks! Does it help if you bodge the translation fault handler along the lines of the untested diff below? Will --->8 diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c index bf1577216ffa..b3c81e448798 100644 --- a/arch/arm/mm/fault.c +++ b/arch/arm/mm/fault.c @@ -407,7 +407,7 @@ do_translation_fault(unsigned long addr, unsigned int fsr, if (addr < TASK_SIZE) return do_page_fault(addr, fsr, regs); - if (user_mode(regs)) + if (user_mode(regs) || fsr_fs(fsr) == FSR_FS_INVALID_PAGE) goto bad_area; index = pgd_index(addr); diff --git a/arch/arm/mm/fault.h b/arch/arm/mm/fault.h index 9ecc2097a87a..8fb26f85e361 100644 --- a/arch/arm/mm/fault.h +++ b/arch/arm/mm/fault.h @@ -12,6 +12,8 @@ #define FSR_FS3_0 (15) #define FSR_FS5_0 (0x3f) +#define FSR_FS_INVALID_PAGE 7 + #ifdef CONFIG_ARM_LPAE #define FSR_FS_AEA 17 diff --git a/arch/arm/mm/fsr-2level.c b/arch/arm/mm/fsr-2level.c index f2be95197265..c7060da345df 100644 --- a/arch/arm/mm/fsr-2level.c +++ b/arch/arm/mm/fsr-2level.c @@ -11,7 +11,7 @@ static struct fsr_info fsr_info[] = { { do_bad, SIGBUS, 0, "external abort on linefetch" }, { do_translation_fault, SIGSEGV, SEGV_MAPERR, "section translation fault" }, { do_bad, SIGBUS, 0, "external abort on linefetch" }, - { do_page_fault, SIGSEGV, SEGV_MAPERR, "page translation fault" }, + { do_translation_fault, SIGSEGV, SEGV_MAPERR, "page translation fault" }, { do_bad, SIGBUS, 0, "external abort on non-linefetch" }, { do_bad, SIGSEGV, SEGV_ACCERR, "section domain fault" }, { do_bad, SIGBUS, 0, "external abort on non-linefetch" }, diff --git a/arch/arm/mm/fsr-3level.c b/arch/arm/mm/fsr-3level.c index d0ae2963656a..19df4af828bd 100644 --- a/arch/arm/mm/fsr-3level.c +++ b/arch/arm/mm/fsr-3level.c @@ -7,7 +7,7 @@ static struct fsr_info fsr_info[] = { { do_bad, SIGBUS, 0, "reserved translation fault" }, { do_translation_fault, SIGSEGV, SEGV_MAPERR, "level 1 translation fault" }, { do_translation_fault, SIGSEGV, SEGV_MAPERR, "level 2 translation fault" }, - { do_page_fault, SIGSEGV, SEGV_MAPERR, "level 3 translation fault" }, + { do_translation_fault, SIGSEGV, SEGV_MAPERR, "level 3 translation fault" }, { do_bad, SIGBUS, 0, "reserved access flag fault" }, { do_bad, SIGSEGV, SEGV_ACCERR, "level 1 access flag fault" }, { do_page_fault, SIGSEGV, SEGV_ACCERR, "level 2 access flag fault" },