From 4e79752c25ec221ac1e28f8875b539ed7631a0db Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 7 Nov 2012 13:35:32 -0800 Subject: 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: [] sysfs_write_file+0x3f/0x160 [ 125.781233] #1: (s_active#94){.+.+.+}, at: [] sysfs_write_file+0xc8/0x160 [ 125.781339] #2: (pm_mutex){+.+.+.}, at: [] pm_suspend+0x81/0x230 [ 125.781439] #3: (tasklist_lock){.?.?..}, at: [] 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] [] lockdep_rcu_suspicious+0x103/0x140 [ 125.781719] [] sched_show_task+0x121/0x180 [ 125.781770] [] try_to_freeze_tasks+0x394/0x3f0 [ 125.781823] [] freeze_kernel_threads+0x25/0x80 [ 125.781876] [] pm_suspend+0x165/0x230 [ 125.781924] [] state_store+0x99/0x100 [ 125.781975] [] kobj_attr_store+0x17/0x20 [ 125.782038] [] sysfs_write_file+0xe1/0x160 [ 125.782091] [] vfs_write+0xc6/0x180 [ 125.782138] [] sys_write+0x5a/0xa0 [ 125.782185] [] ? trace_hardirqs_on_thunk+0x3a/0x3f [ 125.782242] [] system_call_fastpath+0x16/0x1b This commit therefore adds the needed RCU read-side critical section. Reported-by: "Rafael J. Wysocki" Signed-off-by: Paul E. McKenney --- kernel/sched/core.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 6d4569e0924d..36f260864f65 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); -- cgit v1.2.3-59-g8ed1b