From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCH] ioprio: grab rcu_read_lock in sys_ioprio_{set,get}() Date: Mon, 15 Nov 2010 10:15:26 +0100 Message-ID: <4CE0FA2E.9070001@kernel.dk> References: <1289547167-32675-1-git-send-email-gthelen@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Andrew Morton , Oleg Nesterov , "Paul E. McKenney" , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org To: Greg Thelen Return-path: In-Reply-To: <1289547167-32675-1-git-send-email-gthelen@google.com> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On 2010-11-12 08:32, Greg Thelen wrote: > Using: > - CONFIG_LOCKUP_DETECTOR=y > - CONFIG_PREEMPT=y > - CONFIG_LOCKDEP=y > - CONFIG_PROVE_LOCKING=y > - CONFIG_PROVE_RCU=y > found a missing rcu lock during boot on a 512 MiB x86_64 ubuntu vm: > =================================================== > [ INFO: suspicious rcu_dereference_check() usage. ] > --------------------------------------------------- > kernel/pid.c:419 invoked rcu_dereference_check() without protection! > > other info that might help us debug this: > > rcu_scheduler_active = 1, debug_locks = 0 > 1 lock held by ureadahead/1355: > #0: (tasklist_lock){.+.+..}, at: [] sys_ioprio_set+0x7f/0x29e > > stack backtrace: > Pid: 1355, comm: ureadahead Not tainted 2.6.37-dbg-DEV #1 > Call Trace: > [] lockdep_rcu_dereference+0xaa/0xb3 > [] find_task_by_pid_ns+0x44/0x5d > [] find_task_by_vpid+0x22/0x24 > [] sys_ioprio_set+0xb4/0x29e > [] ? trace_hardirqs_off_thunk+0x3a/0x3c > [] sysenter_dispatch+0x7/0x2c > [] ? trace_hardirqs_on_thunk+0x3a/0x3f > > The fix is to: > a) grab rcu lock in sys_ioprio_{set,get}() and > b) avoid grabbing tasklist_lock. > Discussion in: http://marc.info/?l=linux-kernel&m=128951324702889 Thanks Greg, applied. -- Jens Axboe -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org