From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9BD411AACF for ; Mon, 15 Jan 2024 20:58:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 18C0FC433C7; Mon, 15 Jan 2024 20:58:35 +0000 (UTC) Date: Mon, 15 Jan 2024 15:58:33 -0500 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Linus Torvalds , Ajay Kaher , Al Viro , Christian Brauner Subject: Re: [for-next][PATCH 2/3] eventfs: Stop using dcache_readdir() for getdents() Message-ID: <20240115155833.57c9a38b@rorschach.local.home> In-Reply-To: <20240104164738.483305222@goodmis.org> References: <20240104164703.808999991@goodmis.org> <20240104164738.483305222@goodmis.org> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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 Content-Transfer-Encoding: 7bit On Thu, 04 Jan 2024 11:47:05 -0500 Steven Rostedt wrote: > From: "Steven Rostedt (Google)" > > The eventfs creates dynamically allocated dentries and inodes. Using the > dcache_readdir() logic for its own directory lookups requires hiding the > cursor of the dcache logic and playing games to allow the dcache_readdir() > to still have access to the cursor while the eventfs saved what it created > and what it needs to release. > > Instead, just have eventfs have its own iterate_shared callback function > that will fill in the dent entries. This simplifies the code quite a bit. > > Link: https://lore.kernel.org/linux-trace-kernel/20240104015435.682218477@goodmis.org So now I know why Ajay did what he did with the dcach_dir_open_wrapper(): https://lore.kernel.org/all/202401152142.bfc28861-oliver.sang@intel.com/ Basically it crashed with: > [ 41.602625][ T4377] kernel BUG at fs/dcache.c:2031! > [ 41.602625][ T4374] RSP: 0018:ffa000000fcdfcd0 EFLAGS: 00010286 > [ 41.602629][ T4374] RAX: 0000000000000002 RBX: ff11000109392980 RCX: 0000000000000000 > [ 41.602630][ T4374] RDX: 0000000000000000 RSI: ff1100405e46c6f0 RDI: ff1100405f05afc0 > [ 41.602631][ T4374] RBP: ff1100405f05afc0 R08: ffffffff830ad0e0 R09: 0000000000000000 > [ 41.602632][ T4374] R10: 0000000000000280 R11: ffffffff8162036a R12: 0000000000000000 > [ 41.602633][ T4374] R13: ff1100405e46c6f0 R14: ff1100405f05aff8 R15: 0000000000000000 > [ 41.602634][ T4374] FS: 00007f2582ff9740(0000) GS:ff1100407fa80000(0000) knlGS:0000000000000000 > [ 41.602635][ T4374] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 41.602635][ T4374] CR2: 00005624511f3328 CR3: 000000208a342006 CR4: 0000000000771ef0 > [ 41.602636][ T4374] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 41.602637][ T4374] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 41.602638][ T4374] PKRU: 55555554 > [ 41.602638][ T4374] Call Trace: > [ 41.602640][ T4374] > [ 41.602642][ T4374] ? die (arch/x86/kernel/dumpstack.c:421 arch/x86/kernel/dumpstack.c:434 arch/x86/kernel/dumpstack.c:447) > [ 41.602644][ T4374] ? do_trap (arch/x86/kernel/traps.c:112 arch/x86/kernel/traps.c:153) > [ 41.602645][ T4374] ? d_instantiate (fs/dcache.c:2031 (discriminator 1)) > [ 41.602647][ T4374] ? do_error_trap (arch/x86/include/asm/traps.h:59 arch/x86/kernel/traps.c:174) > [ 41.602648][ T4374] ? d_instantiate (fs/dcache.c:2031 (discriminator 1)) > [ 41.602649][ T4374] ? exc_invalid_op (arch/x86/kernel/traps.c:265) > [ 41.602652][ T4374] ? d_instantiate (fs/dcache.c:2031 (discriminator 1)) > [ 41.602653][ T4374] ? asm_exc_invalid_op (arch/x86/include/asm/idtentry.h:568) > [ 41.602655][ T4374] ? tracefs_alloc_inode (fs/tracefs/inode.c:38) > [ 41.602657][ T4374] ? d_instantiate (fs/dcache.c:2031 (discriminator 1)) > [ 41.602659][ T4374] create_dir_dentry (fs/tracefs/event_inode.c:329 fs/tracefs/event_inode.c:516) > [ 41.602661][ T4374] eventfs_root_lookup (fs/tracefs/event_inode.c:611) > [ 41.602662][ T4374] ? terminate_walk (fs/namei.c:691) > [ 41.602665][ T4374] __lookup_slow (fs/namei.c:1694) > [ 41.602667][ T4374] lookup_one_len (fs/namei.c:2746 (discriminator 1)) > [ 41.602669][ T4374] eventfs_start_creating (fs/tracefs/inode.c:536) > [ 41.602671][ T4374] create_dir_dentry (fs/tracefs/event_inode.c:309 fs/tracefs/event_inode.c:516) > [ 41.602673][ T4374] eventfs_iterate (fs/tracefs/event_inode.c:701) > [ 41.602674][ T4374] ? atime_needs_update (fs/inode.c:1842 fs/inode.c:1994) > [ 41.602677][ T4374] iterate_dir (fs/readdir.c:106) > [ 41.602680][ T4374] __x64_sys_getdents (fs/readdir.c:323 fs/readdir.c:307 fs/readdir.c:307) > [ 41.602682][ T4374] ? __pfx_filldir (fs/readdir.c:260) > [ 41.602684][ T4374] do_syscall_64 (arch/x86/entry/common.c:51 arch/x86/entry/common.c:82) > [ 41.602686][ T4374] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:129) I guess that's because I'm creating the inodes and dentries in the iterare_shared() and not at open. The inodes and dentries are created with a ref count of zero, as they should be freed when no longer used. But I don't think the getdents() can handle that in the iterator part. I do need to create the inodes/dentries in the open, up their ref count and dec the ref counts at the release. But I still do not need the dcache_readdir() code to do it. I just have to create an array of inodes to use at the open (like the code did before this update), and have the iterate_shared() use that array, and then the release just decrement the inodes/dentries. I'm off today, so I will likely fix that tomorrow. -- Steve