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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 00721157ae682-78e6a2161bcsm1378637b3.25.2025.12.11.21.15.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Dec 2025 21:15:49 -0800 (PST) Date: Thu, 11 Dec 2025 21:15:37 -0800 (PST) From: Hugh Dickins To: Al Viro cc: Hugh Dickins , Christian Brauner , Andrew Morton , Baolin Wang , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: 6.19 tmpfs __d_lookup() lockup In-Reply-To: <20251212050225.GD1712166@ZenIV> Message-ID: <7f288332-5514-e2ed-69e2-50c5e0304d92@google.com> References: <47e9d03c-7a50-2c7d-247d-36f95a5329ed@google.com> <20251212050225.GD1712166@ZenIV> 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 On Fri, 12 Dec 2025, Al Viro wrote: > On Thu, Dec 11, 2025 at 07:56:38PM -0800, Hugh Dickins wrote: > > > Of course, 2313598222f9 ("convert ramfs and tmpfs") (of Feb 26 2024!) > > comes out as the first failing commit, no surprise there. > > > > I did try inserting a BUG_ON(node == node->next) on line 2438 of > > fs/dcache.c, just after __d_lookup's hlist_bl_for_each_entry_rcu(), > > and that BUG was immediately hit (but, for all I know, perhaps that's > > an unreliable asserition, perhaps it's acceptable for a race to result > > in a momentary node == node->next there). > > Hmm... Could you check if we are somehow hitting d_in_lookup(dentry) > in d_make_persistent()? Am I being stupid and misunderstanding you? I haven't tried running with any printks, it seems obvious from the source that d_make_persistent() always calls __d_instantiate(), which has a WARN_ON(d_in_lookup(dentry)) at the start. But I didn't see that warning fire on any occasion. Hugh