We'll need to use smp_function_call() in the sampling routines, and the call is not supposed to be called from the bottom halves. So, let's convert vmevent to dffered workqueues.
As a side effect, we also fix the swap reporting (we cannot call si_swapinfo from the interrupt context), i.e. the following oops should be fixed now:
================================= [ INFO: inconsistent lock state ] 3.4.0-rc1+ #37 Not tainted --------------------------------- inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. swapper/0/0 [HC0[0]:SC1[1]:HE1:SE0] takes: (swap_lock){+.?...}, at: [<ffffffff8110449d>] si_swapinfo+0x1d/0x90 {SOFTIRQ-ON-W} state was registered at: [<ffffffff8107ca7f>] mark_irqflags+0x15f/0x1b0 [<ffffffff8107e5e3>] __lock_acquire+0x493/0x9d0 [<ffffffff8107f20e>] lock_acquire+0x9e/0x200 [<ffffffff813e9071>] _raw_spin_lock+0x41/0x50 [<ffffffff8110449d>] si_swapinfo+0x1d/0x90 [<ffffffff8117e7c8>] meminfo_proc_show+0x38/0x3f0 [<ffffffff81141209>] seq_read+0x139/0x3f0 [<ffffffff81174cc6>] proc_reg_read+0x86/0xc0 [<ffffffff8111c19c>] vfs_read+0xac/0x160 [<ffffffff8111c29a>] sys_read+0x4a/0x90 [<ffffffff813ea652>] system_call_fastpath+0x16/0x1b
Signed-off-by: Anton Vorontsov anton.vorontsov@linaro.org --- mm/vmevent.c | 49 ++++++++++++++++++++++++++++--------------------- 1 file changed, 28 insertions(+), 21 deletions(-)
diff --git a/mm/vmevent.c b/mm/vmevent.c index 381e9d1..4ca2a04 100644 --- a/mm/vmevent.c +++ b/mm/vmevent.c @@ -3,7 +3,7 @@ #include <linux/compiler.h> #include <linux/vmevent.h> #include <linux/syscalls.h> -#include <linux/timer.h> +#include <linux/workqueue.h> #include <linux/file.h> #include <linux/list.h> #include <linux/poll.h> @@ -34,7 +34,7 @@ struct vmevent_watch { struct vmevent_attr *config_attrs[VMEVENT_CONFIG_MAX_ATTRS];
/* sampling */ - struct timer_list timer; + struct delayed_work work;
/* poll */ wait_queue_head_t waitq; @@ -146,15 +146,13 @@ static bool vmevent_match(struct vmevent_watch *watch) }
/* - * 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. + * This function is called from a workqueue, which can have only one + * execution thread, 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. + * We also don't need to worry about several instances of us accessing + * the same vmevent_watch, as we allocate vmevent_watch together w/ the + * work instance in vmevent_fd(), so there is always one work per + * vmevent_watch. * * All the above makes it possible to implement the lock-free logic, * using just the atomic watch->pending variable. @@ -178,26 +176,35 @@ static void vmevent_sample(struct vmevent_watch *watch) atomic_set(&watch->pending, 1); }
-static void vmevent_timer_fn(unsigned long data) +static void vmevent_schedule_watch(struct vmevent_watch *watch) { - struct vmevent_watch *watch = (struct vmevent_watch *)data; + schedule_delayed_work(&watch->work, + nsecs_to_jiffies64(watch->config.sample_period_ns)); +} + +static struct vmevent_watch *work_to_vmevent_watch(struct work_struct *work) +{ + struct delayed_work *wk = to_delayed_work(work); + + return container_of(wk, struct vmevent_watch, work); +} + +static void vmevent_timer_fn(struct work_struct *work) +{ + struct vmevent_watch *watch = work_to_vmevent_watch(work);
vmevent_sample(watch);
if (atomic_read(&watch->pending)) wake_up(&watch->waitq); - mod_timer(&watch->timer, jiffies + - nsecs_to_jiffies64(watch->config.sample_period_ns)); + + vmevent_schedule_watch(watch); }
static void vmevent_start_timer(struct vmevent_watch *watch) { - init_timer_deferrable(&watch->timer); - watch->timer.data = (unsigned long)watch; - watch->timer.function = vmevent_timer_fn; - watch->timer.expires = jiffies + - nsecs_to_jiffies64(watch->config.sample_period_ns); - add_timer(&watch->timer); + INIT_DELAYED_WORK_DEFERRABLE(&watch->work, vmevent_timer_fn); + vmevent_schedule_watch(watch); }
static unsigned int vmevent_poll(struct file *file, poll_table *wait) @@ -259,7 +266,7 @@ static int vmevent_release(struct inode *inode, struct file *file) { struct vmevent_watch *watch = file->private_data;
- del_timer_sync(&watch->timer); + cancel_delayed_work_sync(&watch->work);
kfree(watch);