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 416DF38F65C; Thu, 8 Oct 2026 17:08:13 +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=1791479295; cv=none; b=mxvv8DFLFPgTS9Paom/fMZmWgRX55Eo12TZ/arOx3l1ICAzdcR6Bx1qIPXwz9/Dcslx0cBY4Slgo+Fm5Vit7lUORQQDZSb5lemems9SWnZT3umZ+u44K8Yey8j5RHxKQXDlgNSZpb+t+UPDGt7vDvnbPwqw1pmiFgUz+fV8bCps= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791479295; c=relaxed/simple; bh=0eBtMTu0/gfhzOhtCIIjYp5dd3J2nx+mqrVP8/rXKb4=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=dmfGvSX2JhHgujMuEkYAU2zJpKM7y3Fpek9DYt2q8Y/9iwafV2sVi5bSTf63kYVrkPOEQ+zvDGmzhMiEwH8hfpUccHVcRsxP2Tz71IwhEKGMWzLhqDtx1DDgus1w9EO+yGzbF277gRcjB7oS4DQf3UizoX3ne191fYP3SqlzkNs= 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=csdqprA4; 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="csdqprA4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7C96D1F000FF; Thu, 8 Oct 2026 17:08:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1791479293; bh=40UmGtsWvKZUKUpHoZBUqaWRitaTWsYb5pdsjbLrFbc=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=csdqprA4ZZqt4Jvt9d+z8dNJvB443wlcluTVQvjFtrKp8TUZICyWcXqBapadTNldC QdYL+b8STFSRrWvvQ00GgMU8AixHHUkCp4+nWQmHNPkadSFl++BN356EwDBUdtaOTT HrH6+T3//qPRmIo+OQJijugBSP4K/KPyye8l/1aY= Date: Thu, 8 Oct 2026 10:08:12 -0700 From: Andrew Morton To: Joseph Qi Cc: Heming Zhao , Anderson Ferneda , Mark Fasheh , Joel Becker , ocfs2-devel@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] ocfs2: deal with legacy signed dir index name hash values Message-Id: <20261008100812.0969af222022821d4ed72fad@linux-foundation.org> In-Reply-To: <20261008122743.616779-1-joseph.qi@linux.alibaba.com> References: <20261008122743.616779-1-joseph.qi@linux.alibaba.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 8 Oct 2026 20:27:42 +0800 Joseph Qi wrote: > Commit 3bc753c06dd0 ("kbuild: treat char as always unsigned") set > -funsigned-char globally, which changed the result of the naked 'char' > load in str2hashbuf(): > > val = msg[i] + (val << 8); > > A name byte >= 0x80 used to sign-extend and now zero-extends, so > ocfs2_dx_dir_name_hash() computes a different hash pair for every name > containing one. The pair is written into the dx leaf when the entry is > created, so an index built by an older kernel no longer matches and > ocfs2_dx_dir_search() returns -ENOENT for a name that readdir still > lists. > > Search with the current unsigned hash and, on a miss, retry with the > legacy signed one, as ext4 does in commit f3bbac32475b2 ("ext4: deal > with legacy signed xattr name hash values"). New entries are always > indexed under the unsigned hash. Skip the retry when the two hashes > are equal, so that a miss on an ASCII name does not walk the index > twice. > > The retry costs a second walk of the dx tree, so a negative lookup of a > name containing a byte >= 0x80 does twice the work. That is bounded and > worth it, and directories whose dx root is still inline pay nothing > extra, since there the retry only rescans the root block that is already > loaded. Nothing retires it at runtime: a legacy entry keeps its legacy > hash, because neither deleting nor updating an entry rewrites the dx > hash, and the only code that rehashes existing dirents is > ocfs2_expand_inline_dir() on the inline to extent conversion. > Rebuilding the index offline is what removes the cost for good. > > Also spell out the signedness in str2hashbuf() instead of leaving the > current hash to -funsigned-char, as commit 854f0912f813 ("ext4: make > xattr char unsignedness in hash explicit") did, so that both variants > stay correct if this is backported to a kernel without the flag. > > Reported-by: Anderson Ferneda > Link: https://lore.kernel.org/ocfs2-devel/CP5P284MB2780AC2C3C2AB2CF2B6CB7AFBE942@CP5P284MB2780.BRAP284.PROD.OUTLOOK.COM/ > Exposed-by: 3bc753c06dd0 ("kbuild: treat char as always unsigned") > Cc: stable@vger.kernel.org # 6.2+ > Signed-off-by: Joseph Qi > --- > fs/ocfs2/dir.c | 76 ++++++++++++++++++++++++++++++++++++++++++-------- > 1 file changed, 65 insertions(+), 11 deletions(-) > > diff --git a/fs/ocfs2/dir.c b/fs/ocfs2/dir.c > index 55c4a305a282..3f159a20a248 100644 > --- a/fs/ocfs2/dir.c > +++ b/fs/ocfs2/dir.c > @@ -221,7 +221,8 @@ static void TEA_transform(__u32 buf[4], __u32 const in[]) > buf[1] += b1; > } > > -static void str2hashbuf(const char *msg, int len, __u32 *buf, int num) > +static void str2hashbuf(const char *msg, int len, __u32 *buf, int num, > + bool legacy_signed) > { > __u32 pad, val; > int i; > @@ -235,7 +236,10 @@ static void str2hashbuf(const char *msg, int len, __u32 *buf, int num) > for (i = 0; i < len; i++) { > if ((i % 4) == 0) > val = pad; > - val = msg[i] + (val << 8); > + if (legacy_signed) > + val = (signed char)msg[i] + (val << 8); > + else > + val = (unsigned char)msg[i] + (val << 8); > if ((i % 4) == 3) { > *buf++ = val; > val = pad; > @@ -248,8 +252,9 @@ static void str2hashbuf(const char *msg, int len, __u32 *buf, int num) > *buf++ = pad; > } > > -static void ocfs2_dx_dir_name_hash(struct inode *dir, const char *name, int len, > - struct ocfs2_dx_hinfo *hinfo) > +static void __ocfs2_dx_dir_name_hash(struct inode *dir, const char *name, > + int len, struct ocfs2_dx_hinfo *hinfo, > + bool legacy_signed) > { > struct ocfs2_super *osb = OCFS2_SB(dir->i_sb); > const char *p; > @@ -279,7 +284,7 @@ static void ocfs2_dx_dir_name_hash(struct inode *dir, const char *name, int len, > > p = name; > while (len > 0) { > - str2hashbuf(p, len, in, 4); > + str2hashbuf(p, len, in, 4, legacy_signed); > TEA_transform(buf, in); > len -= 16; > p += 16; > @@ -290,6 +295,19 @@ static void ocfs2_dx_dir_name_hash(struct inode *dir, const char *name, int len, > hinfo->minor_hash = buf[1]; > } > > +static void ocfs2_dx_dir_name_hash(struct inode *dir, const char *name, int len, > + struct ocfs2_dx_hinfo *hinfo) > +{ > + __ocfs2_dx_dir_name_hash(dir, name, len, hinfo, false); > +} > + > +static void ocfs2_dx_dir_name_hash_signed(struct inode *dir, const char *name, > + int len, > + struct ocfs2_dx_hinfo *hinfo) > +{ > + __ocfs2_dx_dir_name_hash(dir, name, len, hinfo, true); > +} > + > /* > * bh passed here can be an inode block or a dir data block, depending > * on the inode inline data flag. > @@ -1021,10 +1039,10 @@ static int ocfs2_dx_dir_lookup(struct inode *inode, > return ret; > } > > -static int ocfs2_dx_dir_search(const char *name, int namelen, > - struct inode *dir, > - struct ocfs2_dx_root_block *dx_root, > - struct ocfs2_dir_lookup_result *res) > +static int __ocfs2_dx_dir_search(const char *name, int namelen, > + struct inode *dir, > + struct ocfs2_dx_root_block *dx_root, > + struct ocfs2_dir_lookup_result *res) > { > int ret, i, found; > u64 phys; > @@ -1037,8 +1055,6 @@ static int ocfs2_dx_dir_search(const char *name, int namelen, > struct ocfs2_extent_list *dr_el; > struct ocfs2_dx_entry_list *entry_list; > > - ocfs2_dx_dir_name_hash(dir, name, namelen, &res->dl_hinfo); > - > if (ocfs2_dx_root_inline(dx_root)) { > entry_list = &dx_root->dr_entries; > goto search; > @@ -1135,6 +1151,44 @@ static int ocfs2_dx_dir_search(const char *name, int namelen, > return ret; > } > > +static int ocfs2_dx_dir_search(const char *name, int namelen, > + struct inode *dir, > + struct ocfs2_dx_root_block *dx_root, > + struct ocfs2_dir_lookup_result *res) > +{ > + struct ocfs2_dx_hinfo legacy; > + int ret; > + > + ocfs2_dx_dir_name_hash(dir, name, namelen, &res->dl_hinfo); > + > + ret = __ocfs2_dx_dir_search(name, namelen, dir, dx_root, res); > + if (ret != -ENOENT) > + return ret; > + > + /* > + * Nothing under the current hash. The entry may have been indexed by > + * an older kernel, which sign-extended the name bytes when hashing. > + * New entries are always indexed under the unsigned hash, so only fall > + * back to the legacy signed one when it can actually differ: an ASCII > + * name hashes the same either way, and a genuine miss on one should > + * not have to walk the index twice. > + */ > + ocfs2_dx_dir_name_hash_signed(dir, name, namelen, &legacy); > + if (legacy.major_hash == res->dl_hinfo.major_hash && > + legacy.minor_hash == res->dl_hinfo.minor_hash) > + return ret; > + > + res->dl_hinfo = legacy; > + > + ret = __ocfs2_dx_dir_search(name, namelen, dir, dx_root, res); > + if (ret) > + return ret; > + > + pr_warn_once("ocfs2: directory index with signed name hash\n"); > + > + return 0; > +} > + > static int ocfs2_find_entry_dx(const char *name, int namelen, > struct inode *dir, > struct ocfs2_dir_lookup_result *lookup) > -- > 2.39.3