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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 00721157ae682-78e69ffa216sm1656407b3.15.2025.12.11.21.57.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Dec 2025 21:57:28 -0800 (PST) Date: Thu, 11 Dec 2025 21:57:15 -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: <20251212053452.GE1712166@ZenIV> Message-ID: <8ab63110-38b2-2188-91c5-909addfc9b23@google.com> References: <47e9d03c-7a50-2c7d-247d-36f95a5329ed@google.com> <20251212050225.GD1712166@ZenIV> <20251212053452.GE1712166@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 Fri, Dec 12, 2025 at 05:02:25AM +0000, 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()? > > Another question: is it a CONFIG_UNICODE build and are you running with > casefolding anywhere in the vicinity? If so, does this thing reproduce > without that? > > Because that's one potential area of difference between shmem and ramfs > (as well as just about anything else where tree-in-dcache might be > relevant); if that's where the breakage happens, it would narrow the > things down nicely... No, sad to say, CONFIG_UNICODE is not set. (I see why you're asking, I did notice from the diff that the case-folding stuff in shmem.c used to do something different but now the same in several places; but the case-folding people will have to look out for themselves, it's beyond me.) (And yes, I was being stupid in my previous response: once I looked at how simple d_in_lookup() is, I understood your "hitting"; but at least I gave the right answer, no, that warning does not show up.) Hugh