path: root/kernel/trace
diff options
authorSoumya PN <>2016-05-17 21:31:14 +0530
committerSteven Rostedt <>2016-05-20 13:19:37 -0400
commit6112a300c9e41993cc0dc56ac393743d28381284 (patch)
treebfc725d59bb98e3726c6884add2445c233c64eb7 /kernel/trace
parent91e6f1ce8657795cec83a81090c20cbaa8337c68 (diff)
ftrace: Don't disable irqs when taking the tasklist_lock read_lock
In ftrace.c inside the function alloc_retstack_tasklist() (which will be invoked when function_graph tracing is on) the tasklist_lock is being held as reader while iterating through a list of threads. Here the lock is being held as reader with irqs disabled. The tasklist_lock is never write_locked in interrupt context so it is safe to not disable interrupts for the duration of read_lock in this block which, can be significant, given the block of code iterates through all threads. Hence changing the code to call read_lock() and read_unlock() instead of read_lock_irqsave() and read_unlock_irqrestore(). A similar change was made in commits: 8063e41d2ffc ("tracing: Change syscall_*regfunc() to check PF_KTHREAD and use for_each_process_thread()")' and 3472eaa1f12e ("sched: normalize_rt_tasks(): Don't use _irqsave for tasklist_lock, use task_rq_lock()")' Link: Signed-off-by: Soumya PN <> Signed-off-by: Steven Rostedt <>
Diffstat (limited to 'kernel/trace')
1 files changed, 2 insertions, 3 deletions
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index b1870fbd2b67..a6804823a058 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5713,7 +5713,6 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
int i;
int ret = 0;
- unsigned long flags;
int start = 0, end = FTRACE_RETSTACK_ALLOC_SIZE;
struct task_struct *g, *t;
@@ -5729,7 +5728,7 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
- read_lock_irqsave(&tasklist_lock, flags);
+ read_lock(&tasklist_lock);
do_each_thread(g, t) {
if (start == end) {
ret = -EAGAIN;
@@ -5747,7 +5746,7 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
} while_each_thread(g, t);
- read_unlock_irqrestore(&tasklist_lock, flags);
+ read_unlock(&tasklist_lock);
for (i = start; i < end; i++)