| Message ID | 20121107222233.GG2541@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
On Wednesday, November 07, 2012 02:22:34 PM Paul E. McKenney wrote: > On Fri, Nov 02, 2012 at 04:10:34PM -0700, Linus Torvalds wrote: > > On Fri, Nov 2, 2012 at 3:43 PM, Rafael J. Wysocki <rjw@sisk.pl> wrote: > > > > > > Well, not everything is rosy in the suspend land, though. This is a > > > failure to freeze khubd during the second in a row attempt to suspend to > > > RAM (your current tree): > > > > Ugh. So khubd is blocked in usb_start_wait_urb(), and apparently the > > timeout for that block is longer than the freezing timeout. > > > > There's a comment about why khubd needs to be freezable, but I wonder > > if that whole thing isn't doing something wrong. Causing the suspend > > to fail is definitely always the wrong thing. > > > > Greg? > > > > > [ 125.780766] [ INFO: suspicious RCU usage. ] > > > [ 125.780804] 3.7.0-rc3+ #988 Not tainted > > > [ 125.780838] ------------------------------- > > > [ 125.780875] /home/rafael/src/linux/kernel/sched/core.c:4497 suspicious rcu_dereference_check() usage! > > > > Heh. The RCU usage is from the debug printout from sched_show_task(), > > so it's "related", but it's a totally independent issue. > > > > It's apparently because we've not done a "rcu_read_lock()" around that > > sequence, but I seriously doubt we care. But it's technically a real > > bug - even if the fix might be to just not print out the parent pid > > (or to just ignore the bug and turn the rcu dereference into an > > ACCESS_ONCE() or something. > > > > Ingo, Peter, any comments about that sched/core.c:4497 RCU usage? > > Rafael, does the following patch fix that problem? Well, the box I can reproduce that on is not with me now and it's not readily reproducible anyway, so it may take some time to verify I'm afraid. Thanks, Rafael > ------------------------------------------------------------------------ > > sched: Mark RCU reader in sched_show_task() > > When sched_show_task() is invoked from try_to_freeze_tasks(), there is > no RCU read-side critical section, resulting in the following splat: > > [ 125.780730] =============================== > [ 125.780766] [ INFO: suspicious RCU usage. ] > [ 125.780804] 3.7.0-rc3+ #988 Not tainted > [ 125.780838] ------------------------------- > [ 125.780875] /home/rafael/src/linux/kernel/sched/core.c:4497 suspicious rcu_dereference_check() usage! > [ 125.780946] > [ 125.780946] other info that might help us debug this: > [ 125.780946] > [ 125.781031] > [ 125.781031] rcu_scheduler_active = 1, debug_locks = 0 > [ 125.781087] 4 locks held by s2ram/4211: > [ 125.781120] #0: (&buffer->mutex){+.+.+.}, at: [<ffffffff811e2acf>] sysfs_write_file+0x3f/0x160 > [ 125.781233] #1: (s_active#94){.+.+.+}, at: [<ffffffff811e2b58>] sysfs_write_file+0xc8/0x160 > [ 125.781339] #2: (pm_mutex){+.+.+.}, at: [<ffffffff81090a81>] pm_suspend+0x81/0x230 > [ 125.781439] #3: (tasklist_lock){.?.?..}, at: [<ffffffff8108feed>] try_to_freeze_tasks+0x2cd/0x3f0 > [ 125.781543] > [ 125.781543] stack backtrace: > [ 125.781584] Pid: 4211, comm: s2ram Not tainted 3.7.0-rc3+ #988 > [ 125.781632] Call Trace: > [ 125.781662] [<ffffffff810a3c73>] lockdep_rcu_suspicious+0x103/0x140 > [ 125.781719] [<ffffffff8107cf21>] sched_show_task+0x121/0x180 > [ 125.781770] [<ffffffff8108ffb4>] try_to_freeze_tasks+0x394/0x3f0 > [ 125.781823] [<ffffffff810903b5>] freeze_kernel_threads+0x25/0x80 > [ 125.781876] [<ffffffff81090b65>] pm_suspend+0x165/0x230 > [ 125.781924] [<ffffffff8108fa29>] state_store+0x99/0x100 > [ 125.781975] [<ffffffff812f5867>] kobj_attr_store+0x17/0x20 > [ 125.782038] [<ffffffff811e2b71>] sysfs_write_file+0xe1/0x160 > [ 125.782091] [<ffffffff811667a6>] vfs_write+0xc6/0x180 > [ 125.782138] [<ffffffff81166ada>] sys_write+0x5a/0xa0 > [ 125.782185] [<ffffffff812ff6ae>] ? trace_hardirqs_on_thunk+0x3a/0x3f > [ 125.782242] [<ffffffff81669dd2>] system_call_fastpath+0x16/0x1b > > This commit therefore adds the needed RCU read-side critical section. > > Reported-by: "Rafael J. Wysocki" <rjw@sisk.pl> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 6d4569e..36f2608 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4474,6 +4474,7 @@ static const char stat_nam[] = TASK_STATE_TO_CHAR_STR; > void sched_show_task(struct task_struct *p) > { > unsigned long free = 0; > + int ppid; > unsigned state; > > state = p->state ? __ffs(p->state) + 1 : 0; > @@ -4493,8 +4494,11 @@ void sched_show_task(struct task_struct *p) > #ifdef CONFIG_DEBUG_STACK_USAGE > free = stack_not_used(p); > #endif > + rcu_read_lock(); > + ppid = task_pid_nr(rcu_dereference(p->real_parent)); > + rcu_read_unlock(); > printk(KERN_CONT "%5lu %5d %6d 0x%08lx\n", free, > - task_pid_nr(p), task_pid_nr(rcu_dereference(p->real_parent)), > + task_pid_nr(p), ppid, > (unsigned long)task_thread_info(p)->flags); > > show_stack(p, NULL); > >
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 6d4569e..36f2608 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4474,6 +4474,7 @@ static const char stat_nam[] = TASK_STATE_TO_CHAR_STR; void sched_show_task(struct task_struct *p) { unsigned long free = 0; + int ppid; unsigned state; state = p->state ? __ffs(p->state) + 1 : 0; @@ -4493,8 +4494,11 @@ void sched_show_task(struct task_struct *p) #ifdef CONFIG_DEBUG_STACK_USAGE free = stack_not_used(p); #endif + rcu_read_lock(); + ppid = task_pid_nr(rcu_dereference(p->real_parent)); + rcu_read_unlock(); printk(KERN_CONT "%5lu %5d %6d 0x%08lx\n", free, - task_pid_nr(p), task_pid_nr(rcu_dereference(p->real_parent)), + task_pid_nr(p), ppid, (unsigned long)task_thread_info(p)->flags); show_stack(p, NULL);