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="HQmorr4b" 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 7A418BF; Mon, 27 Nov 2023 08:14:44 -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=f6t3S95m3XiCuv2fnCK3LYrmUiIo2p7MxZyJA3+p7Vk=; b=HQmorr4bydMgYYjt+87IfrdCnX wkoemiCdFgrYV+AgikhFuQfsaBscVGISJO9sIzM9L5j5Sf1tWzj5a1OTTd0CI6mr1f0CU1iCeyFNF U8jQAg6oXDXjuqa5M8plGosyofibiF7dLCRysFq3mA9AiGEZfQJY/NNCYi5ILyA2qC/BM4qym/YkV V7O5lUkYKtkyDX0RA2ywbV+uLIn16rVbmCspIYFwM2X8BhdgLYH6nN2hbhn2ZchAPDjtx1J58cwMP nLnW1m0Rnq93mc8agBKsoiTJuhLCYvxOboHF/V0XVMJ0nx/OY7F3s47E7HJ6wXGumDcr/eLt+3Myz /D/tjinw==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1r7eFe-00434D-22; Mon, 27 Nov 2023 16:14:26 +0000 Date: Mon, 27 Nov 2023 16:14:26 +0000 From: Al Viro To: "Eric W. Biederman" Cc: Gabriel Krisman Bertazi , 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, Miklos Szeredi Subject: Re: fun with d_invalidate() vs. d_splice_alias() was Re: [f2fs-dev] [PATCH v6 0/9] Support negative dentries on case-insensitive ext4 and f2fs Message-ID: <20231127161426.GA964333@ZenIV> References: <20231123171255.GN38156@ZenIV> <20231123182426.GO38156@ZenIV> <20231123215234.GQ38156@ZenIV> <20231125220136.GB38156@ZenIV> <20231126045219.GD38156@ZenIV> <20231126184141.GF38156@ZenIV> <20231127063842.GG38156@ZenIV> <87jzq3nqos.fsf@email.froward.int.ebiederm.org> <20231127160318.GI38156@ZenIV> 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: <20231127160318.GI38156@ZenIV> Sender: Al Viro On Mon, Nov 27, 2023 at 04:03:18PM +0000, Al Viro wrote: > On Mon, Nov 27, 2023 at 09:47:47AM -0600, Eric W. Biederman wrote: > > > There is a lot going on there. I remember one of the relevant > > restrictions was marking dentries dont_mount, and inodes S_DEAD > > in unlink and rmdir. > > > > But even without out that marking if d_invalidate is called > > from d_revalidate the inode and all of it's dentries must be > > dead because the inode is stale and most go. There should > > be no resurrecting it at that point. > > > > I suspect the most fruitful way to think of the d_invalidate vs > > d_splice_alias races is an unlink vs rename race. > > > > I don't think the mechanism matters, but deeply and fundamentally > > if we detect a directory inode is dead we need to stick with > > that decision and not attempt to resurrect it with d_splice_alias. > > Wrong. Deeply and fundamentally we detect a dentry that does not > match the directory contents according to the server. > > For example, due to rename done on server. With object in question > perfectly alive there - fhandle still works, etc. > > However, it's no longer where it used to be. And we would bloody better > not have lookups for the old name result in access to that object. > We also should never allow the access to *new* name lead to two live > dentries for the same directory inode. > > Again, this is not about rmdir() or unlink() - invalidation can happen > for object that is still open, still accessed and still very much alive. > Does that all the time for any filesystem with ->d_revalidate(). Put another way, there used to be very odd song and dance in ->d_revalidate() instances along the lines of "we can't possibly tell the caller to invalidate a mountpoint"; it was racy in the best case and during the rewrite of d_invalidate() to teach it how to evict submounts those attempts had been dropped - ->d_revalidate() returning 0 does end up with mounts dissolved by d_invalidate() from caller. It always had been racy, starting with the checks that used to be in ->d_revalidate() instances way before all those changes. So the switch of d_invalidate() to dissolving submounts had been a step in the right direction, but it's not being careful enough. Again, it's about d_invalidate() caused by pathwalk running into a dentry that doesn't match the reality vs. d_splice_alias() finding that it matches the inode we had looked up elsewhere.