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authorThomas Gleixner <tglx@linutronix.de>2011-05-20 16:18:50 +0200
committerThomas Gleixner <tglx@linutronix.de>2011-05-23 13:59:53 +0200
commit9ec2690758a5467f24beb301cca5098078073bba (patch)
treee5bc78f690d12635a56460ea6f54b49318221dc8 /fs
parent250f972d85effad5b6e10da4bbd877e6a4b503b6 (diff)
timerfd: Manage cancelable timers in timerfd
Peter is concerned about the extra scan of CLOCK_REALTIME_COS in the timer interrupt. Yes, I did not think about it, because the solution was so elegant. I didn't like the extra list in timerfd when it was proposed some time ago, but with a rcu based list the list walk it's less horrible than the original global lock, which was held over the list iteration. Requested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Peter Zijlstra <peterz@infradead.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/timerfd.c105
1 files changed, 74 insertions, 31 deletions
diff --git a/fs/timerfd.c b/fs/timerfd.c
index 7e14c9e7c4e..f67acbdda5e 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -22,6 +22,7 @@
#include <linux/anon_inodes.h>
#include <linux/timerfd.h>
#include <linux/syscalls.h>
+#include <linux/rcupdate.h>
struct timerfd_ctx {
struct hrtimer tmr;
@@ -31,9 +32,14 @@ struct timerfd_ctx {
u64 ticks;
int expired;
int clockid;
+ struct rcu_head rcu;
+ struct list_head clist;
bool might_cancel;
};
+static LIST_HEAD(cancel_list);
+static DEFINE_SPINLOCK(cancel_lock);
+
/*
* This gets called when the timer event triggers. We set the "expired"
* flag, but we do not re-arm the timer (in case it's necessary,
@@ -53,28 +59,69 @@ static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
return HRTIMER_NORESTART;
}
-static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
+/*
+ * Called when the clock was set to cancel the timers in the cancel
+ * list.
+ */
+void timerfd_clock_was_set(void)
{
- ktime_t remaining;
+ ktime_t moffs = ktime_get_monotonic_offset();
+ struct timerfd_ctx *ctx;
+ unsigned long flags;
- remaining = hrtimer_expires_remaining(&ctx->tmr);
- return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
+ rcu_read_lock();
+ list_for_each_entry_rcu(ctx, &cancel_list, clist) {
+ if (!ctx->might_cancel)
+ continue;
+ spin_lock_irqsave(&ctx->wqh.lock, flags);
+ if (ctx->moffs.tv64 != moffs.tv64) {
+ ctx->moffs.tv64 = KTIME_MAX;
+ wake_up_locked(&ctx->wqh);
+ }
+ spin_unlock_irqrestore(&ctx->wqh.lock, flags);
+ }
+ rcu_read_unlock();
}
-static bool timerfd_canceled(struct timerfd_ctx *ctx)
+static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
{
- ktime_t moffs;
+ if (ctx->might_cancel) {
+ ctx->might_cancel = false;
+ spin_lock(&cancel_lock);
+ list_del_rcu(&ctx->clist);
+ spin_unlock(&cancel_lock);
+ }
+}
- if (!ctx->might_cancel)
+static bool timerfd_canceled(struct timerfd_ctx *ctx)
+{
+ if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
return false;
+ ctx->moffs = ktime_get_monotonic_offset();
+ return true;
+}
- moffs = ktime_get_monotonic_offset();
+static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
+{
+ if (ctx->clockid == CLOCK_REALTIME && (flags & TFD_TIMER_ABSTIME) &&
+ (flags & TFD_TIMER_CANCEL_ON_SET)) {
+ if (!ctx->might_cancel) {
+ ctx->might_cancel = true;
+ spin_lock(&cancel_lock);
+ list_add_rcu(&ctx->clist, &cancel_list);
+ spin_unlock(&cancel_lock);
+ }
+ } else if (ctx->might_cancel) {
+ timerfd_remove_cancel(ctx);
+ }
+}
- if (moffs.tv64 == ctx->moffs.tv64)
- return false;
+static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
+{
+ ktime_t remaining;
- ctx->moffs = moffs;
- return true;
+ remaining = hrtimer_expires_remaining(&ctx->tmr);
+ return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
}
static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
@@ -87,13 +134,6 @@ static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
htmode = (flags & TFD_TIMER_ABSTIME) ?
HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
- ctx->might_cancel = false;
- if (htmode == HRTIMER_MODE_ABS && ctx->clockid == CLOCK_REALTIME &&
- (flags & TFD_TIMER_CANCELON_SET)) {
- clockid = CLOCK_REALTIME_COS;
- ctx->might_cancel = true;
- }
-
texp = timespec_to_ktime(ktmr->it_value);
ctx->expired = 0;
ctx->ticks = 0;
@@ -113,8 +153,9 @@ static int timerfd_release(struct inode *inode, struct file *file)
{
struct timerfd_ctx *ctx = file->private_data;
+ timerfd_remove_cancel(ctx);
hrtimer_cancel(&ctx->tmr);
- kfree(ctx);
+ kfree_rcu(ctx, rcu);
return 0;
}
@@ -149,20 +190,20 @@ static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
else
res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
+ /*
+ * If clock has changed, we do not care about the
+ * ticks and we do not rearm the timer. Userspace must
+ * reevaluate anyway.
+ */
+ if (timerfd_canceled(ctx)) {
+ ctx->ticks = 0;
+ ctx->expired = 0;
+ res = -ECANCELED;
+ }
+
if (ctx->ticks) {
ticks = ctx->ticks;
- /*
- * If clock has changed, we do not care about the
- * ticks and we do not rearm the timer. Userspace must
- * reevaluate anyway.
- */
- if (timerfd_canceled(ctx)) {
- ticks = 0;
- ctx->expired = 0;
- res = -ECANCELED;
- }
-
if (ctx->expired && ctx->tintv.tv64) {
/*
* If tintv.tv64 != 0, this is a periodic timer that
@@ -258,6 +299,8 @@ SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
return PTR_ERR(file);
ctx = file->private_data;
+ timerfd_setup_cancel(ctx, flags);
+
/*
* We need to stop the existing timer before reprogramming
* it to the new values.