[PATCH 04/11] exit: Deal with nested sleeps

Peter Zijlstra
2014-09-24T08:27:15Z

[-- Attachment #1: peterz-might_sleep-exit.patch --]
[-- Type: text/plain, Size: 2625 bytes --]

do_wait() is a big wait loop, but we set TASK_RUNNING too late; we end
up calling potential sleeps before we reset it.

Not strictly a bug since we're guaranteed to exit the loop and not
call schedule(); put in annotations to quiet might_sleep().

WARNING: CPU: 0 PID: 1 at ../kernel/sched/core.c:7123 __might_sleep+0x7e/0x90()
do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffff8109a788>] do_wait+0x88/0x270

Call Trace:
[<ffffffff81694991>] dump_stack+0x4e/0x7a
[<ffffffff8109877c>] warn_slowpath_common+0x8c/0xc0
[<ffffffff8109886c>] warn_slowpath_fmt+0x4c/0x50
[<ffffffff810bca6e>] __might_sleep+0x7e/0x90
[<ffffffff811a1c15>] might_fault+0x55/0xb0
[<ffffffff8109a3fb>] wait_consider_task+0x90b/0xc10
[<ffffffff8109a804>] do_wait+0x104/0x270
[<ffffffff8109b837>] SyS_wait4+0x77/0x100
[<ffffffff8169d692>] system_call_fastpath+0x16/0x1b

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/kernel.h | 2 ++
kernel/exit.c | 5 +++++
2 files changed, 7 insertions(+)

--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -175,10 +175,12 @@ extern int _cond_resched(void);
*/
# define might_sleep() \
do { __might_sleep(__FILE__, __LINE__, 0); might_resched(); } while (0)
+# define fixup_sleep() __set_current_state(TASK_RUNNING)
#else
static inline void __might_sleep(const char *file, int line,
int preempt_offset) { }
# define might_sleep() do { might_resched(); } while (0)
+# define fixup_sleep() do { } while (0)
#endif

#define might_sleep_if(cond) do { if (cond) might_sleep(); } while (0)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -997,6 +997,8 @@ static int wait_task_zombie(struct wait_

get_task_struct(p);
read_unlock(&tasklist_lock);
+ fixup_sleep();
+
if ((exit_code & 0x7f) == 0) {
why = CLD_EXITED;
status = exit_code >> 8;
@@ -1079,6 +1081,7 @@ static int wait_task_zombie(struct wait_
* thread can reap it because we its state == DEAD/TRACE.
*/
read_unlock(&tasklist_lock);
+ fixup_sleep();

retval = wo->wo_rusage
? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
@@ -1210,6 +1213,7 @@ static int wait_task_stopped(struct wait
pid = task_pid_vnr(p);
why = ptrace ? CLD_TRAPPED : CLD_STOPPED;
read_unlock(&tasklist_lock);
+ fixup_sleep();

if (unlikely(wo->wo_flags & WNOWAIT))
return wait_noreap_copyout(wo, p, pid, uid, why, exit_code);
@@ -1272,6 +1276,7 @@ static int wait_task_continued(struct wa
pid = task_pid_vnr(p);
get_task_struct(p);
read_unlock(&tasklist_lock);
+ fixup_sleep();

if (!wo->wo_info) {
retval = wo->wo_rusage