vmevent grabs a mutex in the atomic context, and so this pops up:
BUG: sleeping function called from invalid context at kernel/mutex.c:271 in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0 1 lock held by swapper/0/0: #0: (&watch->timer){+.-...}, at: [<ffffffff8103eb80>] call_timer_fn+0x0/0xf0 Pid: 0, comm: swapper/0 Not tainted 3.2.0+ #6 Call Trace: <IRQ> [<ffffffff8102f5da>] __might_sleep+0x12a/0x1e0 [<ffffffff810bd990>] ? vmevent_match+0xe0/0xe0 [<ffffffff81321f2c>] mutex_lock_nested+0x3c/0x340 [<ffffffff81064b33>] ? lock_acquire+0xa3/0xc0 [<ffffffff8103eb80>] ? internal_add_timer+0x110/0x110 [<ffffffff810bd990>] ? vmevent_match+0xe0/0xe0 [<ffffffff810bda21>] vmevent_timer_fn+0x91/0xf0 [<ffffffff810bd990>] ? vmevent_match+0xe0/0xe0 [<ffffffff8103ebf5>] call_timer_fn+0x75/0xf0 [<ffffffff8103eb80>] ? internal_add_timer+0x110/0x110 [<ffffffff81062fdd>] ? trace_hardirqs_on_caller+0x7d/0x120 [<ffffffff8103ee9f>] run_timer_softirq+0x10f/0x1e0 [<ffffffff810bd990>] ? vmevent_match+0xe0/0xe0 [<ffffffff81038d90>] __do_softirq+0xb0/0x160 [<ffffffff8105eb0f>] ? tick_program_event+0x1f/0x30 [<ffffffff8132642c>] call_softirq+0x1c/0x26 [<ffffffff810036d5>] do_softirq+0x85/0xc0
This patch fixes the issue by removing the mutex and making the logic lock-free.
Signed-off-by: Anton Vorontsov anton.vorontsov@linaro.org --- mm/vmevent.c | 52 ++++++++++++++++++++++++++-------------------------- 1 file changed, 26 insertions(+), 26 deletions(-)
diff --git a/mm/vmevent.c b/mm/vmevent.c index 1847b56..9ed6aca 100644 --- a/mm/vmevent.c +++ b/mm/vmevent.c @@ -1,4 +1,5 @@ #include <linux/anon_inodes.h> +#include <linux/atomic.h> #include <linux/vmevent.h> #include <linux/syscalls.h> #include <linux/timer.h> @@ -22,8 +23,7 @@ struct vmevent_watch_event { struct vmevent_watch { struct vmevent_config config;
- struct mutex mutex; - bool pending; + atomic_t pending;
/* * Attributes that are exported as part of delivered VM events. @@ -99,24 +99,36 @@ static bool vmevent_match(struct vmevent_watch *watch) return false; }
+/* + * This function is called from the timer context, which has the same + * guaranties as an interrupt handler: it can have only one execution + * thread (unlike bare softirq handler), so we don't need to worry + * about racing w/ ourselves. + * + * We also don't need to worry about several instances of timers + * accessing the same vmevent_watch, as we allocate vmevent_watch + * together w/ the timer instance in vmevent_fd(), so there is always + * one timer per vmevent_watch. + * + * All the above makes it possible to implement the lock-free logic, + * using just the atomic watch->pending variable. + */ static void vmevent_sample(struct vmevent_watch *watch) { int i;
+ if (atomic_read(&watch->pending)) + return; if (!vmevent_match(watch)) return;
- mutex_lock(&watch->mutex); - - watch->pending = true; - for (i = 0; i < watch->nr_attrs; i++) { struct vmevent_attr *attr = &watch->sample_attrs[i];
attr->value = vmevent_sample_attr(watch, attr); }
- mutex_unlock(&watch->mutex); + atomic_set(&watch->pending, 1); }
static void vmevent_timer_fn(unsigned long data) @@ -125,7 +137,7 @@ static void vmevent_timer_fn(unsigned long data)
vmevent_sample(watch);
- if (watch->pending) + if (atomic_read(&watch->pending)) wake_up(&watch->waitq); mod_timer(&watch->timer, jiffies + nsecs_to_jiffies64(watch->config.sample_period_ns)); @@ -148,13 +160,9 @@ static unsigned int vmevent_poll(struct file *file, poll_table *wait)
poll_wait(file, &watch->waitq, wait);
- mutex_lock(&watch->mutex); - - if (watch->pending) + if (atomic_read(&watch->pending)) events |= POLLIN;
- mutex_unlock(&watch->mutex); - return events; }
@@ -171,15 +179,13 @@ static ssize_t vmevent_read(struct file *file, char __user *buf, size_t count, l if (count < size) return -EINVAL;
- mutex_lock(&watch->mutex); - - if (!watch->pending) - goto out_unlock; + if (!atomic_read(&watch->pending)) + goto out;
event = kmalloc(size, GFP_KERNEL); if (!event) { ret = -ENOMEM; - goto out_unlock; + goto out; }
for (i = 0; i < watch->nr_attrs; i++) { @@ -195,14 +201,10 @@ static ssize_t vmevent_read(struct file *file, char __user *buf, size_t count, l
ret = count;
- watch->pending = false; - + atomic_set(&watch->pending, 0); out_free: kfree(event); - -out_unlock: - mutex_unlock(&watch->mutex); - +out: return ret; }
@@ -231,8 +233,6 @@ static struct vmevent_watch *vmevent_watch_alloc(void) if (!watch) return NULL;
- mutex_init(&watch->mutex); - init_waitqueue_head(&watch->waitq);
return watch;