[RESEND][PATCH v3 01/17] notifier: Fix broken error handling pattern

From: Peter Zijlstra
Date: Tue Mar 24 2020 - 10:25:46 EST

The current notifiers have the following error handling pattern all
over the place:

int err, nr;

err = __foo_notifier_call_chain(&chain, val_up, v, -1, &nr);
if (err & NOTIFIER_STOP_MASK)
__foo_notifier_call_chain(&chain, val_down, v, nr-1, NULL)

And aside from the endless repetition thereof, it is broken. Consider
blocking notifiers; both calls take and drop the rwsem, this means
that the notifier list can change in between the two calls, making @nr
meaningless.

Fix this by replacing all the __foo_notifier_call_chain() functions
with foo_notifier_call_chain_robust() that embeds the above pattern,
but ensures it is inside a single lock region.

Note: I switched atomic_notifier_call_chain_robust() to use
the spinlock, since RCU cannot provide the guarantee
required for the recovery.

Note: software_resume() error handling was broken afaict.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
---
include/linux/notifier.h | 15 +--
kernel/cpu_pm.c | 48 ++++--------
kernel/notifier.c | 144 ++++++++++++++++++++++---------------
kernel/power/hibernate.c | 26 +++---
kernel/power/main.c | 8 +-
kernel/power/power.h | 3
kernel/power/suspend.c | 14 +--
kernel/power/user.c | 14 +--
tools/power/pm-graph/sleepgraph.py | 2
9 files changed, 141 insertions(+), 133 deletions(-)

--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -161,20 +161,19 @@ extern int srcu_notifier_chain_unregiste

extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
unsigned long val, void *v);
-extern int __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
- unsigned long val, void *v, int nr_to_call, int *nr_calls);
extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
unsigned long val, void *v);
-extern int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
- unsigned long val, void *v, int nr_to_call, int *nr_calls);
extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
unsigned long val, void *v);
-extern int __raw_notifier_call_chain(struct raw_notifier_head *nh,
- unsigned long val, void *v, int nr_to_call, int *nr_calls);
extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
unsigned long val, void *v);
-extern int __srcu_notifier_call_chain(struct srcu_notifier_head *nh,
- unsigned long val, void *v, int nr_to_call, int *nr_calls);
+
+extern int atomic_notifier_call_chain_robust(struct atomic_notifier_head *nh,
+ unsigned long val_up, unsigned long val_down, void *v);
+extern int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh,
+ unsigned long val_up, unsigned long val_down, void *v);
+extern int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
+ unsigned long val_up, unsigned long val_down, void *v);

#define NOTIFY_DONE 0x0000 /* Don't care */
#define NOTIFY_OK 0x0001 /* Suits me */
--- a/kernel/cpu_pm.c
+++ b/kernel/cpu_pm.c
@@ -15,18 +15,28 @@

static ATOMIC_NOTIFIER_HEAD(cpu_pm_notifier_chain);

-static int cpu_pm_notify(enum cpu_pm_event event, int nr_to_call, int *nr_calls)
+static int cpu_pm_notify(enum cpu_pm_event event)
{
int ret;

/*
- * __atomic_notifier_call_chain has a RCU read critical section, which
+ * atomic_notifier_call_chain has a RCU read critical section, which
* could be disfunctional in cpu idle. Copy RCU_NONIDLE code to let
* RCU know this.
*/
rcu_irq_enter_irqson();
- ret = __atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL,
- nr_to_call, nr_calls);
+ ret = atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL);
+ rcu_irq_exit_irqson();
+
+ return notifier_to_errno(ret);
+}
+
+static int cpu_pm_notify_robust(enum cpu_pm_event event_up, enum cpu_pm_event event_down)
+{
+ int ret;
+
+ rcu_irq_enter_irqson();
+ ret = atomic_notifier_call_chain_robust(&cpu_pm_notifier_chain, event_up, event_down, NULL);
rcu_irq_exit_irqson();

return notifier_to_errno(ret);
@@ -80,18 +90,7 @@ EXPORT_SYMBOL_GPL(cpu_pm_unregister_noti
*/
int cpu_pm_enter(void)
{
- int nr_calls;
- int ret = 0;
-
- ret = cpu_pm_notify(CPU_PM_ENTER, -1, &nr_calls);
- if (ret)
- /*
- * Inform listeners (nr_calls - 1) about failure of CPU PM
- * PM entry who are notified earlier to prepare for it.
- */
- cpu_pm_notify(CPU_PM_ENTER_FAILED, nr_calls - 1, NULL);
-
- return ret;
+ return cpu_pm_notify_robust(CPU_PM_ENTER, CPU_PM_ENTER_FAILED);
}
EXPORT_SYMBOL_GPL(cpu_pm_enter);

@@ -109,7 +108,7 @@ EXPORT_SYMBOL_GPL(cpu_pm_enter);
*/
int cpu_pm_exit(void)
{
- return cpu_pm_notify(CPU_PM_EXIT, -1, NULL);
+ return cpu_pm_notify(CPU_PM_EXIT);
}
EXPORT_SYMBOL_GPL(cpu_pm_exit);

@@ -131,18 +130,7 @@ EXPORT_SYMBOL_GPL(cpu_pm_exit);
*/
int cpu_cluster_pm_enter(void)
{
- int nr_calls;
- int ret = 0;
-
- ret = cpu_pm_notify(CPU_CLUSTER_PM_ENTER, -1, &nr_calls);
- if (ret)
- /*
- * Inform listeners (nr_calls - 1) about failure of CPU cluster
- * PM entry who are notified earlier to prepare for it.
- */
- cpu_pm_notify(CPU_CLUSTER_PM_ENTER_FAILED, nr_calls - 1, NULL);
-
- return ret;
+ return cpu_pm_notify_robust(CPU_CLUSTER_PM_ENTER, CPU_CLUSTER_PM_ENTER_FAILED);
}
EXPORT_SYMBOL_GPL(cpu_cluster_pm_enter);

@@ -163,7 +151,7 @@ EXPORT_SYMBOL_GPL(cpu_cluster_pm_enter);
*/
int cpu_cluster_pm_exit(void)
{
- return cpu_pm_notify(CPU_CLUSTER_PM_EXIT, -1, NULL);
+ return cpu_pm_notify(CPU_CLUSTER_PM_EXIT);
}
EXPORT_SYMBOL_GPL(cpu_cluster_pm_exit);

--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -94,6 +94,34 @@ static int notifier_call_chain(struct no
}
NOKPROBE_SYMBOL(notifier_call_chain);

+/**
+ * notifier_call_chain_robust - Inform the registered notifiers about an event
+ * and rollback on error.
+ * @nl: Pointer to head of the blocking notifier chain
+ * @val_up: Value passed unmodified to the notifier function
+ * @val_down: Value passed unmodified to the notifier function when recovering
+ * from an error on @val_up
+ * @v Pointer passed unmodified to the notifier function
+ *
+ * NOTE: It is important the @nl chain doesn't change between the two
+ * invocations of notifier_call_chain() such that we visit the
+ * exact same notifier callbacks; this rules out any RCU usage.
+ *
+ * Returns: the return value of the @val_up call.
+ */
+static int notifier_call_chain_robust(struct notifier_block **nl,
+ unsigned long val_up, unsigned long val_down,
+ void *v)
+{
+ int ret, nr = 0;
+
+ ret = notifier_call_chain(nl, val_up, v, -1, &nr);
+ if (ret & NOTIFY_STOP_MASK)
+ notifier_call_chain(nl, val_down, v, nr-1, NULL);
+
+ return ret;
+}
+
/*
* Atomic notifier chain routines. Registration and unregistration
* use a spinlock, and call_chain is synchronized by RCU (no locks).
@@ -144,13 +172,30 @@ int atomic_notifier_chain_unregister(str
}
EXPORT_SYMBOL_GPL(atomic_notifier_chain_unregister);

+int atomic_notifier_call_chain_robust(struct atomic_notifier_head *nh,
+ unsigned long val_up, unsigned long val_down, void *v)
+{
+ unsigned long flags;
+ int ret;
+
+ /*
+ * Musn't use RCU; because then the notifier list can
+ * change between the up and down traversal.
+ */
+ spin_lock_irqsave(&nh->lock, flags);
+ ret = notifier_call_chain_robust(&nh->head, val_up, val_down, v);
+ spin_unlock_irqrestore(&nh->lock, flags);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(atomic_notifier_call_chain_robust);
+NOKPROBE_SYMBOL(atomic_notifier_call_chain_robust);
+
/**
- * __atomic_notifier_call_chain - Call functions in an atomic notifier chain
+ * atomic_notifier_call_chain - Call functions in an atomic notifier chain
* @nh: Pointer to head of the atomic notifier chain
* @val: Value passed unmodified to notifier function
* @v: Pointer passed unmodified to notifier function
- * @nr_to_call: See the comment for notifier_call_chain.
- * @nr_calls: See the comment for notifier_call_chain.
*
* Calls each function in a notifier chain in turn. The functions
* run in an atomic context, so they must not block.
@@ -163,24 +208,16 @@ EXPORT_SYMBOL_GPL(atomic_notifier_chain_
* Otherwise the return value is the return value
* of the last notifier function called.
*/
-int __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
- unsigned long val, void *v,
- int nr_to_call, int *nr_calls)
+int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
+ unsigned long val, void *v)
{
int ret;

rcu_read_lock();
- ret = notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls);
+ ret = notifier_call_chain(&nh->head, val, v, -1, NULL);
rcu_read_unlock();
- return ret;
-}
-EXPORT_SYMBOL_GPL(__atomic_notifier_call_chain);
-NOKPROBE_SYMBOL(__atomic_notifier_call_chain);

-int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
- unsigned long val, void *v)
-{
- return __atomic_notifier_call_chain(nh, val, v, -1, NULL);
+ return ret;
}
EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);
NOKPROBE_SYMBOL(atomic_notifier_call_chain);
@@ -250,13 +287,30 @@ int blocking_notifier_chain_unregister(s
}
EXPORT_SYMBOL_GPL(blocking_notifier_chain_unregister);

+int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh,
+ unsigned long val_up, unsigned long val_down, void *v)
+{
+ int ret = NOTIFY_DONE;
+
+ /*
+ * We check the head outside the lock, but if this access is
+ * racy then it does not matter what the result of the test
+ * is, we re-check the list after having taken the lock anyway:
+ */
+ if (rcu_access_pointer(nh->head)) {
+ down_read(&nh->rwsem);
+ ret = notifier_call_chain_robust(&nh->head, val_up, val_down, v);
+ up_read(&nh->rwsem);
+ }
+ return ret;
+}
+EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_robust);
+
/**
- * __blocking_notifier_call_chain - Call functions in a blocking notifier chain
+ * blocking_notifier_call_chain - Call functions in a blocking notifier chain
* @nh: Pointer to head of the blocking notifier chain
* @val: Value passed unmodified to notifier function
* @v: Pointer passed unmodified to notifier function
- * @nr_to_call: See comment for notifier_call_chain.
- * @nr_calls: See comment for notifier_call_chain.
*
* Calls each function in a notifier chain in turn. The functions
* run in a process context, so they are allowed to block.
@@ -268,9 +322,8 @@ EXPORT_SYMBOL_GPL(blocking_notifier_chai
* Otherwise the return value is the return value
* of the last notifier function called.
*/
-int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
- unsigned long val, void *v,
- int nr_to_call, int *nr_calls)
+int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
+ unsigned long val, void *v)
{
int ret = NOTIFY_DONE;

@@ -281,19 +334,11 @@ int __blocking_notifier_call_chain(struc
*/
if (rcu_access_pointer(nh->head)) {
down_read(&nh->rwsem);
- ret = notifier_call_chain(&nh->head, val, v, nr_to_call,
- nr_calls);
+ ret = notifier_call_chain(&nh->head, val, v, -1, NULL);
up_read(&nh->rwsem);
}
return ret;
}
-EXPORT_SYMBOL_GPL(__blocking_notifier_call_chain);
-
-int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
- unsigned long val, void *v)
-{
- return __blocking_notifier_call_chain(nh, val, v, -1, NULL);
-}
EXPORT_SYMBOL_GPL(blocking_notifier_call_chain);

/*
@@ -335,13 +380,18 @@ int raw_notifier_chain_unregister(struct
}
EXPORT_SYMBOL_GPL(raw_notifier_chain_unregister);

+int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
+ unsigned long val_up, unsigned long val_down, void *v)
+{
+ return notifier_call_chain_robust(&nh->head, val_up, val_down, v);
+}
+EXPORT_SYMBOL_GPL(raw_notifier_call_chain_robust);
+
/**
- * __raw_notifier_call_chain - Call functions in a raw notifier chain
+ * raw_notifier_call_chain - Call functions in a raw notifier chain
* @nh: Pointer to head of the raw notifier chain
* @val: Value passed unmodified to notifier function
* @v: Pointer passed unmodified to notifier function
- * @nr_to_call: See comment for notifier_call_chain.
- * @nr_calls: See comment for notifier_call_chain
*
* Calls each function in a notifier chain in turn. The functions
* run in an undefined context.
@@ -354,18 +404,10 @@ EXPORT_SYMBOL_GPL(raw_notifier_chain_unr
* Otherwise the return value is the return value
* of the last notifier function called.
*/
-int __raw_notifier_call_chain(struct raw_notifier_head *nh,
- unsigned long val, void *v,
- int nr_to_call, int *nr_calls)
-{
- return notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls);
-}
-EXPORT_SYMBOL_GPL(__raw_notifier_call_chain);
-
int raw_notifier_call_chain(struct raw_notifier_head *nh,
unsigned long val, void *v)
{
- return __raw_notifier_call_chain(nh, val, v, -1, NULL);
+ return notifier_call_chain(&nh->head, val, v, -1, NULL);
}
EXPORT_SYMBOL_GPL(raw_notifier_call_chain);

@@ -437,12 +479,10 @@ int srcu_notifier_chain_unregister(struc
EXPORT_SYMBOL_GPL(srcu_notifier_chain_unregister);

/**
- * __srcu_notifier_call_chain - Call functions in an SRCU notifier chain
+ * srcu_notifier_call_chain - Call functions in an SRCU notifier chain
* @nh: Pointer to head of the SRCU notifier chain
* @val: Value passed unmodified to notifier function
* @v: Pointer passed unmodified to notifier function
- * @nr_to_call: See comment for notifier_call_chain.
- * @nr_calls: See comment for notifier_call_chain
*
* Calls each function in a notifier chain in turn. The functions
* run in a process context, so they are allowed to block.
@@ -454,25 +494,17 @@ EXPORT_SYMBOL_GPL(srcu_notifier_chain_un
* Otherwise the return value is the return value
* of the last notifier function called.
*/
-int __srcu_notifier_call_chain(struct srcu_notifier_head *nh,
- unsigned long val, void *v,
- int nr_to_call, int *nr_calls)
+int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
+ unsigned long val, void *v)
{
int ret;
int idx;

idx = srcu_read_lock(&nh->srcu);
- ret = notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls);
+ ret = notifier_call_chain(&nh->head, val, v, -1, NULL);
srcu_read_unlock(&nh->srcu, idx);
return ret;
}
-EXPORT_SYMBOL_GPL(__srcu_notifier_call_chain);
-
-int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
- unsigned long val, void *v)
-{
- return __srcu_notifier_call_chain(nh, val, v, -1, NULL);
-}
EXPORT_SYMBOL_GPL(srcu_notifier_call_chain);

/**
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -694,8 +694,8 @@ static int load_image_and_restore(void)
*/
int hibernate(void)
{
- int error, nr_calls = 0;
bool snapshot_test = false;
+ int error;

if (!hibernation_available()) {
pm_pr_dbg("Hibernation not available.\n");
@@ -711,11 +711,9 @@ int hibernate(void)

pr_info("hibernation entry\n");
pm_prepare_console();
- error = __pm_notifier_call_chain(PM_HIBERNATION_PREPARE, -1, &nr_calls);
- if (error) {
- nr_calls--;
- goto Exit;
- }
+ error = pm_notifier_call_chain_robust(PM_HIBERNATION_PREPARE, PM_POST_HIBERNATION);
+ if (error)
+ goto Restore;

ksys_sync_helper();

@@ -773,7 +771,8 @@ int hibernate(void)
/* Don't bother checking whether freezer_test_done is true */
freezer_test_done = false;
Exit:
- __pm_notifier_call_chain(PM_POST_HIBERNATION, nr_calls, NULL);
+ pm_notifier_call_chain(PM_POST_HIBERNATION);
+ Restore:
pm_restore_console();
atomic_inc(&snapshot_device_available);
Unlock:
@@ -801,7 +800,7 @@ int hibernate(void)
*/
static int software_resume(void)
{
- int error, nr_calls = 0;
+ int error;

/*
* If the user said "noresume".. bail out early.
@@ -888,11 +887,9 @@ static int software_resume(void)

pr_info("resume from hibernation\n");
pm_prepare_console();
- error = __pm_notifier_call_chain(PM_RESTORE_PREPARE, -1, &nr_calls);
- if (error) {
- nr_calls--;
- goto Close_Finish;
- }
+ error = pm_notifier_call_chain_robust(PM_RESTORE_PREPARE, PM_POST_RESTORE);
+ if (error)
+ goto Restore;

pm_pr_dbg("Preparing processes for hibernation restore.\n");
error = freeze_processes();
@@ -901,7 +898,8 @@ static int software_resume(void)
error = load_image_and_restore();
thaw_processes();
Finish:
- __pm_notifier_call_chain(PM_POST_RESTORE, nr_calls, NULL);
+ pm_notifier_call_chain(PM_POST_RESTORE);
+ Restore:
pm_restore_console();
pr_info("resume failed (%d)\n", error);
atomic_inc(&snapshot_device_available);
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -80,18 +80,18 @@ int unregister_pm_notifier(struct notifi
}
EXPORT_SYMBOL_GPL(unregister_pm_notifier);

-int __pm_notifier_call_chain(unsigned long val, int nr_to_call, int *nr_calls)
+int pm_notifier_call_chain_robust(unsigned long val_up, unsigned long val_down)
{
int ret;

- ret = __blocking_notifier_call_chain(&pm_chain_head, val, NULL,
- nr_to_call, nr_calls);
+ ret = blocking_notifier_call_chain_robust(&pm_chain_head, val_up, val_down, NULL);

return notifier_to_errno(ret);
}
+
int pm_notifier_call_chain(unsigned long val)
{
- return __pm_notifier_call_chain(val, -1, NULL);
+ return blocking_notifier_call_chain(&pm_chain_head, val, NULL);
}

/* If set, devices may be suspended and resumed asynchronously. */
--- a/kernel/power/power.h
+++ b/kernel/power/power.h
@@ -210,8 +210,7 @@ static inline void suspend_test_finish(c

#ifdef CONFIG_PM_SLEEP
/* kernel/power/main.c */
-extern int __pm_notifier_call_chain(unsigned long val, int nr_to_call,
- int *nr_calls);
+extern int pm_notifier_call_chain_robust(unsigned long val_up, unsigned long val_down);
extern int pm_notifier_call_chain(unsigned long val);
#endif

--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -342,18 +342,16 @@ static int suspend_test(int level)
*/
static int suspend_prepare(suspend_state_t state)
{
- int error, nr_calls = 0;
+ int error;

if (!sleep_state_supported(state))
return -EPERM;

pm_prepare_console();

- error = __pm_notifier_call_chain(PM_SUSPEND_PREPARE, -1, &nr_calls);
- if (error) {
- nr_calls--;
- goto Finish;
- }
+ error = pm_notifier_call_chain_robust(PM_SUSPEND_PREPARE, PM_POST_SUSPEND);
+ if (error)
+ goto Restore;

trace_suspend_resume(TPS("freeze_processes"), 0, true);
error = suspend_freeze_processes();
@@ -363,8 +361,8 @@ static int suspend_prepare(suspend_state

suspend_stats.failed_freeze++;
dpm_save_failed_step(SUSPEND_FREEZE);
- Finish:
- __pm_notifier_call_chain(PM_POST_SUSPEND, nr_calls, NULL);
+ pm_notifier_call_chain(PM_POST_SUSPEND);
+ Restore:
pm_restore_console();
return error;
}
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -44,7 +44,7 @@ atomic_t snapshot_device_available = ATO
static int snapshot_open(struct inode *inode, struct file *filp)
{
struct snapshot_data *data;
- int error, nr_calls = 0;
+ int error;

if (!hibernation_available())
return -EPERM;
@@ -71,9 +71,7 @@ static int snapshot_open(struct inode *i
swap_type_of(swsusp_resume_device, 0, NULL) : -1;
data->mode = O_RDONLY;
data->free_bitmaps = false;
- error = __pm_notifier_call_chain(PM_HIBERNATION_PREPARE, -1, &nr_calls);
- if (error)
- __pm_notifier_call_chain(PM_POST_HIBERNATION, --nr_calls, NULL);
+ error = pm_notifier_call_chain_robust(PM_HIBERNATION_PREPARE, PM_POST_HIBERNATION);
} else {
/*
* Resuming. We may need to wait for the image device to
@@ -83,15 +81,11 @@ static int snapshot_open(struct inode *i

data->swap = -1;
data->mode = O_WRONLY;
- error = __pm_notifier_call_chain(PM_RESTORE_PREPARE, -1, &nr_calls);
+ error = pm_notifier_call_chain_robust(PM_RESTORE_PREPARE, PM_POST_RESTORE);
if (!error) {
error = create_basic_memory_bitmaps();
data->free_bitmaps = !error;
- } else
- nr_calls--;
-
- if (error)
- __pm_notifier_call_chain(PM_POST_RESTORE, nr_calls, NULL);
+ }
}
if (error)
atomic_inc(&snapshot_device_available);
--- a/tools/power/pm-graph/sleepgraph.py
+++ b/tools/power/pm-graph/sleepgraph.py
@@ -167,7 +167,7 @@ import base64
tracefuncs = {
'sys_sync': {},
'ksys_sync': {},
- '__pm_notifier_call_chain': {},
+ 'pm_notifier_call_chain_robust': {},
'pm_prepare_console': {},
'pm_notifier_call_chain': {},
'freeze_processes': {},