From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="k5omMfob" Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [IPv6:2a03:a000:7:0:5054:ff:fe1c:15ff]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 88096D42; Thu, 23 Nov 2023 09:13:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=1PVt9jFHLZyJOvNOweTTAr+mfv0r2vN5F3uo83rFOeM=; b=k5omMfobXlbs3nKnm6Y7p5XpTM BbyEoJZsEdpf6Kz2bX5ZuyivItc5gUHlbKeRuBPxRO6awg9VMR0KlhgNIfKsRKR/UzRSe/bCClLGL AGcVIHz8vx+E1GluuVF3yiR6oPl5HdWKA3vhlEmuK8jEgrwlQFsFLUbRtnDmoq8sD94sQkGIg9GmC DJg6ZPMC81fe7N8opXMUOA/asv/ZkU4HWTbr250Yb5sF57EqKRbDD0ioVXWfwm6gkHLjL+uZQ3rWx ge51hByqQ+JJaHZeNDYzTBJtG8IbmXbnj/HEEhi81q1VkMk9z1xB/7FcvPIWTJHhPGnvU1ezScJIc 43XIg4vQ==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1r6DG3-002Air-1I; Thu, 23 Nov 2023 17:12:55 +0000 Date: Thu, 23 Nov 2023 17:12:55 +0000 From: Al Viro To: Gabriel Krisman Bertazi Cc: Linus Torvalds , Christian Brauner , tytso@mit.edu, linux-f2fs-devel@lists.sourceforge.net, ebiggers@kernel.org, linux-fsdevel@vger.kernel.org, jaegeuk@kernel.org, linux-ext4@vger.kernel.org Subject: Re: [f2fs-dev] [PATCH v6 0/9] Support negative dentries on case-insensitive ext4 and f2fs Message-ID: <20231123171255.GN38156@ZenIV> References: <20230816050803.15660-1-krisman@suse.de> <20231025-selektiert-leibarzt-5d0070d85d93@brauner> <655a9634.630a0220.d50d7.5063SMTPIN_ADDED_BROKEN@mx.google.com> <20231120-nihilismus-verehren-f2b932b799e0@brauner> <20231121022734.GC38156@ZenIV> <20231122211901.GJ38156@ZenIV> <87o7fkihst.fsf@> 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: <87o7fkihst.fsf@> Sender: Al Viro On Thu, Nov 23, 2023 at 10:57:22AM -0500, Gabriel Krisman Bertazi wrote: > Linus Torvalds writes: > > > Side note: Gabriel, as things are now, instead of that > > > > if (!d_is_casefolded_name(dentry)) > > return 0; > > > > in generic_ci_d_revalidate(), I would suggest that any time a > > directory is turned into a case-folded one, you'd just walk all the > > dentries for that directory and invalidate negative ones at that > > point. Or was there some reason I missed that made it a good idea to > > do it at run-time after-the-fact? > > > > The problem I found with that approach, which I originally tried, was > preventing concurrent lookups from racing with the invalidation and > creating more 'case-sensitive' negative dentries. Did I miss a way to > synchronize with concurrent lookups of the children of the dentry? We > can trivially ensure the dentry doesn't have positive children by > holding the parent lock, but that doesn't protect from concurrent > lookups creating negative dentries, as far as I understand. AFAICS, there is a problem with dentries that never came through ->lookup(). Unless I'm completely misreading your code, your generic_ci_d_revalidate() is not called for them. Ever. Hash lookups are controlled by ->d_op of parent; that's where ->d_hash() and ->d_compare() come from. Revalidate comes from *child*. You need ->d_op->d_revalidate of child dentry to be set to your generic_ci_d_revalidate(). The place where it gets set is generic_set_encrypted_ci_d_ops(). Look at its callchain; in case of ext4 it gets called from ext4_lookup_dentry(), which is called from ext4_lookup(). And dentry passed to it is the argument of ->lookup(). Now take a look at open-by-fhandle stuff; all methods in there (->fh_to_dentry(), ->fh_to_parent(), ->get_parent()) end up returning d_obtain_alias(some inode). We *do* call ->lookup(), all right - in reconnect_one(), while trying to connect those suckers with the main tree. But the way it works is that d_splice_alias() in ext4_lookup() moves the existing alias for subdirectory, connecting it to the parent. That's not the dentry ext4_lookup() had set ->d_op on - that's the dentry that came from d_obtain_alias(). And those do not have ->d_op set by anything in your tree. That's the problem I'd been talking about - there is a class of situations where the work done by ext4_lookup() to set the state of dentry gets completely lost. After lookup you do have a dentry in the right place, with the right name and inode, etc., but with NULL ->d_op->d_revalidate.