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Subject[PATCH 1/3] vmevent: Should not grab mutex in the atomic context
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 | 35 ++++++++++++-----------------------
1 files changed, 12 insertions(+), 23 deletions(-)
diff --git a/mm/vmevent.c b/mm/vmevent.c
index 1847b56..a56174f 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>
@@ -23,7 +24,7 @@ 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.
@@ -103,20 +104,18 @@ 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 +124,7 @@ 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 +147,9 @@ 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 +166,13 @@ 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 +188,10 @@ 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;
}

--
1.7.7.6


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