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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> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 07DEA1C0004 X-Stat-Signature: suhy61p6x9af7t8zw1cux1o7acmsnz1n X-Rspam-User: X-HE-Tag: 1765519049-993188 X-HE-Meta: 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 tkb4Vl+R GqbCQgZ3GFeRXFvWi90jdjTZgzk56vQ+G0vLi25t5cVyorVHhYelyhL80Lc+fNPwOG89RIMzryiiM2anw/uCGui6pvK3GCbwKpz3QNYHAFC7Kt2TvZvHyFukWa1sZ+hyICfjbrm+hN+PvGlMfyb8YYfTJUA/w9LpUu3oKqjQ6nGl7yODbbG2D+5S7nMB5by3aR6a3Xh1AO2eA64ieGDZvVUNJhnvbHGRgqVyOzTH8jU7C+wBb2cjTJbS8af7nN1+cton1tx8e6B5/IaaNO2AlNdJLvn/iP+JeAuiPan/l1WO3aIoBXKNafDDxYx/aWujRn39UTD9bSlMP/n2DIJLVICN53d/iPszBBUdLgl6ExdIabF8m8upZQGrqO3EooNf4EMDcjpMEwAjuB32T5J+yuMdxng== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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