1 files changed, 51 insertions, 6 deletions

diff --git a/fs/timerfd.c b/fs/timerfd.c
index 8c4fc1425b3e..7e14c9e7c4ee 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -26,10 +26,12 @@
 struct timerfd_ctx {
         struct hrtimer tmr;
         ktime_t tintv;
+        ktime_t moffs;
         wait_queue_head_t wqh;
         u64 ticks;
         int expired;
         int clockid;
+        bool might_cancel;
 };
 
 /*
@@ -59,24 +61,52 @@ static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
         return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
 }
 
-static void timerfd_setup(struct timerfd_ctx *ctx, int flags,
-                          const struct itimerspec *ktmr)
+static bool timerfd_canceled(struct timerfd_ctx *ctx)
+{
+        ktime_t moffs;
+
+        if (!ctx->might_cancel)
+                return false;
+
+        moffs = ktime_get_monotonic_offset();
+
+        if (moffs.tv64 == ctx->moffs.tv64)
+                return false;
+
+        ctx->moffs = moffs;
+        return true;
+}
+
+static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
+                         const struct itimerspec *ktmr)
 {
         enum hrtimer_mode htmode;
         ktime_t texp;
+        int clockid = ctx->clockid;
 
         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;
         ctx->tintv = timespec_to_ktime(ktmr->it_interval);
-        hrtimer_init(&ctx->tmr, ctx->clockid, htmode);
+        hrtimer_init(&ctx->tmr, clockid, htmode);
         hrtimer_set_expires(&ctx->tmr, texp);
         ctx->tmr.function = timerfd_tmrproc;
-        if (texp.tv64 != 0)
+        if (texp.tv64 != 0) {
                 hrtimer_start(&ctx->tmr, texp, htmode);
+                if (timerfd_canceled(ctx))
+                        return -ECANCELED;
+        }
+        return 0;
 }
 
 static int timerfd_release(struct inode *inode, struct file *file)
@@ -118,8 +148,21 @@ static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
                 res = -EAGAIN;
         else
                 res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
+
         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
@@ -183,6 +226,7 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
         init_waitqueue_head(&ctx->wqh);
         ctx->clockid = clockid;
         hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
+        ctx->moffs = ktime_get_monotonic_offset();
 
         ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
                                O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
@@ -199,6 +243,7 @@ SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
         struct file *file;
         struct timerfd_ctx *ctx;
         struct itimerspec ktmr, kotmr;
+        int ret;
 
         if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
                 return -EFAULT;
@@ -240,14 +285,14 @@ SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
         /*
          * Re-program the timer to the new value ...
          */
-        timerfd_setup(ctx, flags, &ktmr);
+        ret = timerfd_setup(ctx, flags, &ktmr);
 
         spin_unlock_irq(&ctx->wqh.lock);
         fput(file);
         if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr)))
                 return -EFAULT;
 
-        return 0;
+        return ret;
 }
 
 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)