From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH] ioprio: grab rcu_read_lock in sys_ioprio_{set,get}() Date: Fri, 12 Nov 2010 04:18:33 -0800 Message-ID: <20101112121833.GB2825@linux.vnet.ibm.com> References: <1289547167-32675-1-git-send-email-gthelen@google.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andrew Morton , Oleg Nesterov , Jens Axboe , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org To: Greg Thelen Return-path: Content-Disposition: inline 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 Thu, Nov 11, 2010 at 11:32:47PM -0800, 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 Acked-by: Paul E. McKenney > Signed-off-by: Greg Thelen > --- > fs/ioprio.c | 13 ++++--------- > 1 files changed, 4 insertions(+), 9 deletions(-) > > diff --git a/fs/ioprio.c b/fs/ioprio.c > index 748cfb9..7da2a06 100644 > --- a/fs/ioprio.c > +++ b/fs/ioprio.c > @@ -103,12 +103,7 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio) > } > > ret = -ESRCH; > - /* > - * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic", > - * so we can't use rcu_read_lock(). See re-copy of ->ioprio > - * in copy_process(). > - */ > - read_lock(&tasklist_lock); > + rcu_read_lock(); > switch (which) { > case IOPRIO_WHO_PROCESS: > if (!who) > @@ -153,7 +148,7 @@ free_uid: > ret = -EINVAL; > } > > - read_unlock(&tasklist_lock); > + rcu_read_unlock(); > return ret; > } > > @@ -197,7 +192,7 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who) > int ret = -ESRCH; > int tmpio; > > - read_lock(&tasklist_lock); > + rcu_read_lock(); > switch (which) { > case IOPRIO_WHO_PROCESS: > if (!who) > @@ -250,6 +245,6 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who) > ret = -EINVAL; > } > > - read_unlock(&tasklist_lock); > + rcu_read_unlock(); > return ret; > } > -- > 1.7.3.1 > -- 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