From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 612EBC11F67 for ; Thu, 1 Jul 2021 21:55:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 45AA661416 for ; Thu, 1 Jul 2021 21:55:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234125AbhGAV6T (ORCPT ); Thu, 1 Jul 2021 17:58:19 -0400 Received: from mail.kernel.org ([198.145.29.99]:49790 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229934AbhGAV6S (ORCPT ); Thu, 1 Jul 2021 17:58:18 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 803FA61410; Thu, 1 Jul 2021 21:55:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1625176547; bh=J2pnPixnxsQv3DGjaK8vxbyjUZeAoadH4MR1n52LoKM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=mW7XU+BMNMVA0CQP9AZ7DdFKUdRmW1U+KWD56eN4cRCxe3KNhpUIbSjTEgbXnZaGn m2kNCxmoPpRu6jTkd9as2AU0/Xou8jJfZVqeVcN6F/URSYjJwfDT2YP65aTH2bd4l2 eQo2O+ZQpwbBbP8ij/dsd1Pc9GLZTlEzvtDI+O7gLCm4wYJMuVSFaF+UKX/hpuhUSi usC5J9qBN7dDyoZ4/xBVCurFDRSA5jGkA/fopRawEE0qx7wIDHHBU8hM5sFJ4Oc1HM HhfVpop1bVixo0hDV2kNPlr5uhz2yKUfBY76UE+nnX9rmPA5oCqvYLR3LkYP3DifN3 FfgbxYWHxRH0A== Date: Thu, 1 Jul 2021 16:57:40 -0500 From: "Gustavo A. R. Silva" To: David Sterba Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH] btrfs: add special case to setget helpers for 64k pages Message-ID: <20210701215740.GA12099@embeddedor> References: <20210701160039.12518-1-dsterba@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210701160039.12518-1-dsterba@suse.com> Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Thu, Jul 01, 2021 at 06:00:39PM +0200, David Sterba wrote: > On 64K pages the size of the extent_buffer::pages array is 1 and > compilation with -Warray-bounds warns due to > > kaddr = page_address(eb->pages[idx + 1]); > > when reading byte range crossing page boundary. > > This does never actually overflow the array because on 64K because all > the data fit in one page and bounds are checked by check_setget_bounds. > > To fix the reported overflow and warning add a copy of the non-crossing > read/write code and put it behind a condition that's evaluated at > compile time. That way only one implementation remains due to dead code > elimination. Any chance we can use a flexible-array in struct extent_buffer instead, so all the warnings are removed? Something like this: diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h index 62027f551b44..b82e8b694a3b 100644 --- a/fs/btrfs/extent_io.h +++ b/fs/btrfs/extent_io.h @@ -94,11 +94,11 @@ struct extent_buffer { struct rw_semaphore lock; - struct page *pages[INLINE_EXTENT_BUFFER_PAGES]; struct list_head release_list; #ifdef CONFIG_BTRFS_DEBUG struct list_head leak_list; #endif + struct page *pages[]; }; /* which is actually what is needed in this case to silence the array-bounds warnings: the replacement of the one-element array with a flexible-array member[1] in struct extent_buffer. -- Gustavo [1] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays > > Link: https://lore.kernel.org/lkml/20210623083901.1d49d19d@canb.auug.org.au/ > CC: Gustavo A. R. Silva > Signed-off-by: David Sterba > --- > fs/btrfs/struct-funcs.c | 66 +++++++++++++++++++++++++---------------- > 1 file changed, 41 insertions(+), 25 deletions(-) > > diff --git a/fs/btrfs/struct-funcs.c b/fs/btrfs/struct-funcs.c > index 8260f8bb3ff0..51204b280da8 100644 > --- a/fs/btrfs/struct-funcs.c > +++ b/fs/btrfs/struct-funcs.c > @@ -73,14 +73,18 @@ u##bits btrfs_get_token_##bits(struct btrfs_map_token *token, \ > } \ > token->kaddr = page_address(token->eb->pages[idx]); \ > token->offset = idx << PAGE_SHIFT; \ > - if (oip + size <= PAGE_SIZE) \ > + if (INLINE_EXTENT_BUFFER_PAGES == 1) { \ > return get_unaligned_le##bits(token->kaddr + oip); \ > + } else { \ > + if (oip + size <= PAGE_SIZE) \ > + return get_unaligned_le##bits(token->kaddr + oip); \ > \ > - memcpy(lebytes, token->kaddr + oip, part); \ > - token->kaddr = page_address(token->eb->pages[idx + 1]); \ > - token->offset = (idx + 1) << PAGE_SHIFT; \ > - memcpy(lebytes + part, token->kaddr, size - part); \ > - return get_unaligned_le##bits(lebytes); \ > + memcpy(lebytes, token->kaddr + oip, part); \ > + token->kaddr = page_address(token->eb->pages[idx + 1]); \ > + token->offset = (idx + 1) << PAGE_SHIFT; \ > + memcpy(lebytes + part, token->kaddr, size - part); \ > + return get_unaligned_le##bits(lebytes); \ > + } \ > } \ > u##bits btrfs_get_##bits(const struct extent_buffer *eb, \ > const void *ptr, unsigned long off) \ > @@ -94,13 +98,17 @@ u##bits btrfs_get_##bits(const struct extent_buffer *eb, \ > u8 lebytes[sizeof(u##bits)]; \ > \ > ASSERT(check_setget_bounds(eb, ptr, off, size)); \ > - if (oip + size <= PAGE_SIZE) \ > + if (INLINE_EXTENT_BUFFER_PAGES == 1) { \ > return get_unaligned_le##bits(kaddr + oip); \ > + } else { \ > + if (oip + size <= PAGE_SIZE) \ > + return get_unaligned_le##bits(kaddr + oip); \ > \ > - memcpy(lebytes, kaddr + oip, part); \ > - kaddr = page_address(eb->pages[idx + 1]); \ > - memcpy(lebytes + part, kaddr, size - part); \ > - return get_unaligned_le##bits(lebytes); \ > + memcpy(lebytes, kaddr + oip, part); \ > + kaddr = page_address(eb->pages[idx + 1]); \ > + memcpy(lebytes + part, kaddr, size - part); \ > + return get_unaligned_le##bits(lebytes); \ > + } \ > } \ > void btrfs_set_token_##bits(struct btrfs_map_token *token, \ > const void *ptr, unsigned long off, \ > @@ -124,15 +132,19 @@ void btrfs_set_token_##bits(struct btrfs_map_token *token, \ > } \ > token->kaddr = page_address(token->eb->pages[idx]); \ > token->offset = idx << PAGE_SHIFT; \ > - if (oip + size <= PAGE_SIZE) { \ > + if (INLINE_EXTENT_BUFFER_PAGES == 1) { \ > put_unaligned_le##bits(val, token->kaddr + oip); \ > - return; \ > + } else { \ > + if (oip + size <= PAGE_SIZE) { \ > + put_unaligned_le##bits(val, token->kaddr + oip); \ > + return; \ > + } \ > + put_unaligned_le##bits(val, lebytes); \ > + memcpy(token->kaddr + oip, lebytes, part); \ > + token->kaddr = page_address(token->eb->pages[idx + 1]); \ > + token->offset = (idx + 1) << PAGE_SHIFT; \ > + memcpy(token->kaddr, lebytes + part, size - part); \ > } \ > - put_unaligned_le##bits(val, lebytes); \ > - memcpy(token->kaddr + oip, lebytes, part); \ > - token->kaddr = page_address(token->eb->pages[idx + 1]); \ > - token->offset = (idx + 1) << PAGE_SHIFT; \ > - memcpy(token->kaddr, lebytes + part, size - part); \ > } \ > void btrfs_set_##bits(const struct extent_buffer *eb, void *ptr, \ > unsigned long off, u##bits val) \ > @@ -146,15 +158,19 @@ void btrfs_set_##bits(const struct extent_buffer *eb, void *ptr, \ > u8 lebytes[sizeof(u##bits)]; \ > \ > ASSERT(check_setget_bounds(eb, ptr, off, size)); \ > - if (oip + size <= PAGE_SIZE) { \ > + if (INLINE_EXTENT_BUFFER_PAGES == 1) { \ > put_unaligned_le##bits(val, kaddr + oip); \ > - return; \ > - } \ > + } else { \ > + if (oip + size <= PAGE_SIZE) { \ > + put_unaligned_le##bits(val, kaddr + oip); \ > + return; \ > + } \ > \ > - put_unaligned_le##bits(val, lebytes); \ > - memcpy(kaddr + oip, lebytes, part); \ > - kaddr = page_address(eb->pages[idx + 1]); \ > - memcpy(kaddr, lebytes + part, size - part); \ > + put_unaligned_le##bits(val, lebytes); \ > + memcpy(kaddr + oip, lebytes, part); \ > + kaddr = page_address(eb->pages[idx + 1]); \ > + memcpy(kaddr, lebytes + part, size - part); \ > + } \ > } > > DEFINE_BTRFS_SETGET_BITS(8) > -- > 2.31.1 >