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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> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 5C35DC0003 X-Rspamd-Server: rspam03 X-Stat-Signature: 7cmodik48pcgunits9xmohcothm15197 X-Rspam-User: X-HE-Tag: 1765516551-650829 X-HE-Meta: U2FsdGVkX1+HMGTj0PpTgeSA4Hw1USe5Vu+cPxRknVZy0+y93VnTVRgaRMMC990g2mrVZhOE8zKedOz+hzaDcpgXMvm2yljPMEpApDuB3g9m5OoEhN4j9maMXYoWdsqyaH+3nWivbjFFOba71pcSK1vQvVKjDohs4XqQj9dlaCDsQXlTKbj7tPgZgWy6MI0/lO0dF3QX8WJ/cY5Mio8yx+U/zaDe7zEZgoFqa9DdnoRLjsG6U2olsYKoRk21Fc2Gr+PQRK5dVK9S4/Wdy3fqE2Ncb5tzc4ArFPWwtQ8Csv95jnQytGt6vLFBCEVptiV+1hr8qqHrEDG7770jDEpO89W0hLZG5iW+TVAfuDLFNKkyn5kY6rYtnVgWPKEKGUt3Y5YYCF5LxCICvsF+SQLlBXxeiIEAP1GQL3CGGi6z9g0BAakUwYFG4qgJQCGKkekdjbA02gOS7kCa24mxK8nrLE33OabUGi/0ToAxOfxEjeTylgs9094vkxSeeIJF9/+ZIcnSrZEHryovzuhs7tMZASqESwIAAGudS0qbC46rBMJgJuwhU2sglm+azGOOts6WqgoywPJOipygHy676l4r1VJN49INb7ncZafEItM0ioWhTHinWpWQY1NcOx03BnmMwe+o5WwlRbv/SS/WrvtE4RS2btIWgWzT/Hy3idrkW2HPvdE6WVurHxo6VCbQkCOQaVmWBMyPlNtIuj3MpXC8o3bkFcbMNLNYI0UxGEtcUnOh3eJ6DWei79ob+I60xYr6Zdt6gVXioyrVz7JE/kPokNBJfkgFBmObnlmsxwyOC9GKWS7H1/8IJEIrdnb7gk5WamlMG360FO3d0Sn4/wSUPXk3MLgRq3faLkPv0bIAJNQ5922x+B75JSHiSxKeokJhMDaoPSRkRS4XGm1kObyPkttgAY9fOjUlPtLlktIO5gzvnlo7P7X34+Lc7kDst3mO40Yn83gMDXhRcBZg+uX T0+cfqrg rTSKFBPzV8+ady3Y6jiAfUfmAE+0FCXN99CRNf3oWouFuvRO0V2JqE0a+hum7asqJhYO6KYu1mPdIOPibpBwD0e28ukKSZ0rk10Fu7yX9g/BYRJiigM5ysRd2fsQ99MvWIkqg6Nj4QCX560thjr9WX5OYZrl78hkfxj7lmnKn4NZskWYz4x54wuJF5pOCP4JQMBxlQVXigrzwcPGNt/VJhNRe3yJurGKowefg5WRo3+g9ezUB7iOkAoHL+zO8huVD3HkA5RCWcAWQshicH7Yej//eCoNJVu9yvyfbRV/v3ncdlrDKlNBYlQNRew4q1EwvLf9PZp5XnhAnMDkzg4La8z8TvsWY5uCEPDec+O+q/IgBuCxJ3bfd8YxHQ7M/nP24J2QL6JfGv0qtvmc2zJKOeGB1gw== 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 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