Commit 8a32c441 authored by Tejun Heo's avatar Tejun Heo

freezer: implement and use kthread_freezable_should_stop()

Writeback and thinkpad_acpi have been using thaw_process() to prevent
deadlock between the freezer and kthread_stop(); unfortunately, this
is inherently racy - nothing prevents freezing from happening between
thaw_process() and kthread_stop().

This patch implements kthread_freezable_should_stop() which enters
refrigerator if necessary but is guaranteed to return if
kthread_stop() is invoked.  Both thaw_process() users are converted to
use the new function.

Note that this deadlock condition exists for many of freezable
kthreads.  They need to be converted to use the new should_stop or
freezable workqueue.

Tested with synthetic test case.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarHenrique de Moraes Holschuh <ibm-acpi@hmh.eng.br>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Oleg Nesterov <oleg@redhat.com>
parent a0acae0e
......@@ -2456,8 +2456,9 @@ static int hotkey_kthread(void *data)
u32 poll_mask, event_mask;
unsigned int si, so;
unsigned long t;
unsigned int change_detector, must_reset;
unsigned int change_detector;
unsigned int poll_freq;
bool was_frozen;
mutex_lock(&hotkey_thread_mutex);
......@@ -2488,14 +2489,14 @@ static int hotkey_kthread(void *data)
t = 100; /* should never happen... */
}
t = msleep_interruptible(t);
if (unlikely(kthread_should_stop()))
if (unlikely(kthread_freezable_should_stop(&was_frozen)))
break;
must_reset = try_to_freeze();
if (t > 0 && !must_reset)
if (t > 0 && !was_frozen)
continue;
mutex_lock(&hotkey_thread_data_mutex);
if (must_reset || hotkey_config_change != change_detector) {
if (was_frozen || hotkey_config_change != change_detector) {
/* forget old state on thaw or config change */
si = so;
t = 0;
......@@ -2528,10 +2529,6 @@ exit:
static void hotkey_poll_stop_sync(void)
{
if (tpacpi_hotkey_task) {
if (frozen(tpacpi_hotkey_task) ||
freezing(tpacpi_hotkey_task))
thaw_process(tpacpi_hotkey_task);
kthread_stop(tpacpi_hotkey_task);
tpacpi_hotkey_task = NULL;
mutex_lock(&hotkey_thread_mutex);
......
......@@ -947,7 +947,7 @@ int bdi_writeback_thread(void *data)
trace_writeback_thread_start(bdi);
while (!kthread_should_stop()) {
while (!kthread_freezable_should_stop(NULL)) {
/*
* Remove own delayed wake-up timer, since we are already awake
* and we'll take care of the preriodic write-back.
......@@ -977,8 +977,6 @@ int bdi_writeback_thread(void *data)
*/
schedule();
}
try_to_freeze();
}
/* Flush any work that raced with us exiting */
......
......@@ -47,7 +47,7 @@ static inline bool should_send_signal(struct task_struct *p)
/* Takes and releases task alloc lock using task_lock() */
extern int thaw_process(struct task_struct *p);
extern bool __refrigerator(void);
extern bool __refrigerator(bool check_kthr_stop);
extern int freeze_processes(void);
extern int freeze_kernel_threads(void);
extern void thaw_processes(void);
......@@ -57,7 +57,7 @@ static inline bool try_to_freeze(void)
might_sleep();
if (likely(!freezing(current)))
return false;
return __refrigerator();
return __refrigerator(false);
}
extern bool freeze_task(struct task_struct *p, bool sig_only);
......@@ -180,7 +180,7 @@ static inline void set_freeze_flag(struct task_struct *p) {}
static inline void clear_freeze_flag(struct task_struct *p) {}
static inline int thaw_process(struct task_struct *p) { return 1; }
static inline bool __refrigerator(void) { return false; }
static inline bool __refrigerator(bool check_kthr_stop) { return false; }
static inline int freeze_processes(void) { return -ENOSYS; }
static inline int freeze_kernel_threads(void) { return -ENOSYS; }
static inline void thaw_processes(void) {}
......
......@@ -35,6 +35,7 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
void kthread_bind(struct task_struct *k, unsigned int cpu);
int kthread_stop(struct task_struct *k);
int kthread_should_stop(void);
bool kthread_freezable_should_stop(bool *was_frozen);
void *kthread_data(struct task_struct *k);
int kthreadd(void *unused);
......
......@@ -9,6 +9,7 @@
#include <linux/export.h>
#include <linux/syscalls.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
/*
* freezing is complete, mark current process as frozen
......@@ -23,7 +24,7 @@ static inline void frozen_process(void)
}
/* Refrigerator is place where frozen processes are stored :-). */
bool __refrigerator(void)
bool __refrigerator(bool check_kthr_stop)
{
/* Hmm, should we be allowed to suspend when there are realtime
processes around? */
......@@ -50,7 +51,8 @@ bool __refrigerator(void)
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (!frozen(current))
if (!frozen(current) ||
(check_kthr_stop && kthread_should_stop()))
break;
was_frozen = true;
schedule();
......
......@@ -58,6 +58,31 @@ int kthread_should_stop(void)
}
EXPORT_SYMBOL(kthread_should_stop);
/**
* kthread_freezable_should_stop - should this freezable kthread return now?
* @was_frozen: optional out parameter, indicates whether %current was frozen
*
* kthread_should_stop() for freezable kthreads, which will enter
* refrigerator if necessary. This function is safe from kthread_stop() /
* freezer deadlock and freezable kthreads should use this function instead
* of calling try_to_freeze() directly.
*/
bool kthread_freezable_should_stop(bool *was_frozen)
{
bool frozen = false;
might_sleep();
if (unlikely(freezing(current)))
frozen = __refrigerator(true);
if (was_frozen)
*was_frozen = frozen;
return kthread_should_stop();
}
EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
/**
* kthread_data - return data value specified on kthread creation
* @task: kthread task in question
......
......@@ -600,14 +600,10 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
/*
* Finally, kill the kernel thread. We don't need to be RCU
* safe anymore, since the bdi is gone from visibility. Force
* unfreeze of the thread before calling kthread_stop(), otherwise
* it would never exet if it is currently stuck in the refrigerator.
* safe anymore, since the bdi is gone from visibility.
*/
if (bdi->wb.task) {
thaw_process(bdi->wb.task);
if (bdi->wb.task)
kthread_stop(bdi->wb.task);
}
}
/*
......
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