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 85B851171A for ; Mon, 21 Aug 2023 20:08:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 07D80C433C7; Mon, 21 Aug 2023 20:08:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1692648514; bh=ZnKMC5MA3sHAFGoGNIOugIvGhd6Ei9kuQwossqRfee4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fibcfppEw1elFAAbO2MpckM+EyM4MmTqJFF3sHGcYn4LItVuPrZvsfyFfIE6ohl05 I1M2V1vDzUGb36ii94WdT9HkyLwR3DXq4UnVuJ2tepr48HxLTl9SUmSon86T6OyAAh /RzDgMnzyy2d6CLG+4yWF7SAhevnsfEdKOkkUMoo= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Russell Harmon , "Paulo Alcantara (SUSE)" , David Howells , Steve French Subject: [PATCH 6.4 203/234] cifs: Release folio lock on fscache read hit. Date: Mon, 21 Aug 2023 21:42:46 +0200 Message-ID: <20230821194137.833000408@linuxfoundation.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230821194128.754601642@linuxfoundation.org> References: <20230821194128.754601642@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Russell Harmon via samba-technical commit 69513dd669e243928f7450893190915a88f84a2b upstream. Under the current code, when cifs_readpage_worker is called, the call contract is that the callee should unlock the page. This is documented in the read_folio section of Documentation/filesystems/vfs.rst as: > The filesystem should unlock the folio once the read has completed, > whether it was successful or not. Without this change, when fscache is in use and cache hit occurs during a read, the page lock is leaked, producing the following stack on subsequent reads (via mmap) to the page: $ cat /proc/3890/task/12864/stack [<0>] folio_wait_bit_common+0x124/0x350 [<0>] filemap_read_folio+0xad/0xf0 [<0>] filemap_fault+0x8b1/0xab0 [<0>] __do_fault+0x39/0x150 [<0>] do_fault+0x25c/0x3e0 [<0>] __handle_mm_fault+0x6ca/0xc70 [<0>] handle_mm_fault+0xe9/0x350 [<0>] do_user_addr_fault+0x225/0x6c0 [<0>] exc_page_fault+0x84/0x1b0 [<0>] asm_exc_page_fault+0x27/0x30 This requires a reboot to resolve; it is a deadlock. Note however that the call to cifs_readpage_from_fscache does mark the page clean, but does not free the folio lock. This happens in __cifs_readpage_from_fscache on success. Releasing the lock at that point however is not appropriate as cifs_readahead also calls cifs_readpage_from_fscache and *does* unconditionally release the lock after its return. This change therefore effectively makes cifs_readpage_worker work like cifs_readahead. Signed-off-by: Russell Harmon Acked-by: Paulo Alcantara (SUSE) Reviewed-by: David Howells Cc: stable@vger.kernel.org Signed-off-by: Steve French Signed-off-by: Greg Kroah-Hartman --- fs/smb/client/file.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/fs/smb/client/file.c +++ b/fs/smb/client/file.c @@ -4681,9 +4681,9 @@ static int cifs_readpage_worker(struct f io_error: kunmap(page); - unlock_page(page); read_complete: + unlock_page(page); return rc; }