[{"id":3679888,"web_url":"http://patchwork.ozlabs.org/comment/3679888/","msgid":"","list_archive_url":null,"date":"2026-04-21T13:10:15","subject":"Re: [PATCH] smb: client: fix (remove) drop_dir_cache module parameter","submitter":{"id":86063,"url":"http://patchwork.ozlabs.org/api/people/86063/","name":"Bharath SM","email":"bharathsm.hsk@gmail.com"},"content":"Thanks Enzo for fixing this.\n\nOn Tue, Apr 21, 2026 at 5:46 AM Enzo Matsumiya wrote:\n>\n> Being a module parameter, it's possible to do:\n>\n> # modprobe cifs drop_dir_cache=1\n>\n> Which will lead to a crash, because cifs_tcp_ses_list hasn't been\n> initialized yet:\n>\n> [ 168.242624] BUG: kernel NULL pointer dereference, address: 0000000000000010\n> [ 168.242952] #PF: supervisor read access in kernel mode\n> [ 168.243175] #PF: error_code(0x0000) - not-present page\n> [ 168.243394] PGD 0 P4D 0\n> [ 168.243524] Oops: Oops: 0000 [#1] SMP NOPTI\n> [ 168.243703] CPU: 2 UID: 0 PID: 1105 Comm: modprobe Not tainted 7.0.0-lku #5 PREEMPT(lazy)\n> [ 168.244054] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-2-g4f253b9b-prebuilt.qemu.org 04/01/2014\n> [ 168.244557] RIP: 0010:cifs_param_set_drop_dir_cache+0x7c/0x100 [cifs]\n> ...\n> [ 168.248785] Call Trace:\n> [ 168.248915] \n> [ 168.249023] parse_args+0x285/0x3a0\n> [ 168.249204] ? __pfx_unknown_module_param_cb+0x10/0x10\n> [ 168.249448] load_module+0x192b/0x1bb0\n> [ 168.249637] ? __pfx_unknown_module_param_cb+0x10/0x10\n> [ 168.249882] ? kernel_read_file+0x27d/0x2b0\n> [ 168.250088] init_module_from_file+0xce/0xf0\n> [ 168.250291] idempotent_init_module+0xfb/0x2f0\n> [ 168.250496] __x64_sys_finit_module+0x5a/0xa0\n> [ 168.250694] do_syscall_64+0xe0/0x5a0\n> [ 168.250863] ? exc_page_fault+0x65/0x160\n> [ 168.251050] entry_SYSCALL_64_after_hwframe+0x77/0x7f\n> [ 168.251284] RIP: 0033:0x7fcaa12b774d\n>\n> Instead of fixing this with some kind of \"is module initialized\"\n> approach, this patch instead moves that functionality to procfs,\n> setting a write op for the existing open_dirs entry, where\n> writing a 0 to it will drop the cached directory entries.\n>\n> Also make it available only when CONFIG_CIFS_DEBUG2=y.\nCan you please let me know it needs to be under CONFIG_CIFS_DEBUG2,\nI prefer it to be under CONFIG_CIFS_DEBUG as most distros\ndisable the CONFIG_CIFS_DEBUG2.\nThis parameter might be helpful in customer environments to mitigate issues in\ncases if we hit rare directory lease bugs which might keep dirs open.\nPlease let me know your thoughts.?","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linux-cifs@vger.kernel.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=bz/i7sZ3;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org\n (client-ip=2600:3c0a:e001:db::12fc:5321; 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Tue, 21 Apr 2026\n 06:10:26 -0700 (PDT)","Precedence":"bulk","X-Mailing-List":"linux-cifs@vger.kernel.org","List-Id":"","List-Subscribe":"","List-Unsubscribe":"","MIME-Version":"1.0","References":"<20260421170524.266984-1-ematsumiya@suse.de>","In-Reply-To":"<20260421170524.266984-1-ematsumiya@suse.de>","From":"Bharath SM ","Date":"Tue, 21 Apr 2026 06:10:15 -0700","X-Gm-Features":"AQROBzDig4NL35bjPk6k6JlX3OyFSErPAoXBS0dKZ02PHiVw5XYwT2x_0CMAm30","Message-ID":"\n ","Subject":"Re: [PATCH] smb: client: fix (remove) drop_dir_cache module parameter","To":"Enzo Matsumiya ","Cc":"linux-cifs@vger.kernel.org, smfrench@gmail.com, pc@manguebit.com,\n\tronniesahlberg@gmail.com, sprasad@microsoft.com, tom@talpey.com,\n\tbharathsm@microsoft.com, henrique.carvalho@suse.com","Content-Type":"text/plain; charset=\"UTF-8\"","Content-Transfer-Encoding":"quoted-printable"}}]