Re: [Y2038] [PATCH v2] Staging: fbtbt: Replace timespec with ktime_t

On Wednesday 30 September 2015 18:10:49 Ksenija Stanojevic wrote:

struct timespec will overflow in year 2038, so replace it with ktime_t. And replace functions that use struct timespec, timespec_sub with ktime_sub. Also use monotonic time instead of real time, by replacing getnstimeofday with ktime_get, to be more robust against leap seconds and settimeofday() calls. diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c index 7f5fa3d..a1645e1 100644 --- a/drivers/staging/fbtft/fbtft-core.c +++ b/drivers/staging/fbtft/fbtft-core.c @@ -365,16 +365,15 @@ static void fbtft_update_display(struct fbtft_par *par, unsigned start_line, unsigned end_line) { size_t offset, len;

• struct timespec ts_start, ts_end, ts_fps, ts_duration;
• long fps_ms, fps_us, duration_ms, duration_us;
• long fps, throughput;

• ktime_t ts_start, ts_end, ts_fps;
• long long fps, throughput;

Here you declare fps and throughput as 'long long', which causes problems later:

@@ -411,30 +410,22 @@ static void fbtft_update_display(struct fbtft_par *par, unsigned start_line, __func__); if (unlikely(timeit)) {

• getnstimeofday(&ts_end);
  

• if (par->update_time.tv_nsec == 0 && par->update_time.tv_sec == 0) {
  

• 	par->update_time.tv_sec = ts_start.tv_sec;
  

• 	par->update_time.tv_nsec = ts_start.tv_nsec;
  

• }
  

• ts_fps = timespec_sub(ts_start, par->update_time);
  

• par->update_time.tv_sec = ts_start.tv_sec;
  

• par->update_time.tv_nsec = ts_start.tv_nsec;
  

• fps_ms = (ts_fps.tv_sec * 1000) + ((ts_fps.tv_nsec / 1000000) % 1000);
  

• fps_us = (ts_fps.tv_nsec / 1000) % 1000;
  

• fps = fps_ms * 1000 + fps_us;
  

• ts_end = ktime_get();
  

• if (par->update_time.tv64 == 0)
  

• 	par->update_time = ts_start;
  

It's better not to access the 'tv64' field of the ktime_t directly, this is supposed to be hidden. Just use ktime_to_ns() to do the same thing.

• ts_fps = ktime_sub(ts_start, par->update_time);
  

• par->update_time = ts_start;
  

• fps = ktime_to_us(ts_fps);
  

This can be written slightly simpler using the ktime_us_delta() function, like you do below.

fps = fps ? 1000000 / fps : 0;

• ts_duration = timespec_sub(ts_end, ts_start);
  

• duration_ms = (ts_duration.tv_sec * 1000) + ((ts_duration.tv_nsec / 1000000) % 1000);
  

• duration_us = (ts_duration.tv_nsec / 1000) % 1000;
  

• throughput = duration_ms * 1000 + duration_us;
  

• throughput = ktime_us_delta(ts_end, ts_start);
  

  throughput = throughput ? (len * 1000) / throughput : 0; throughput = throughput * 1000 / 1024;

As mentioned above, throughput is a 64-bit 'long long', so the last line of the context will result in a 64-bit division, which is not allowed in 32-bit kernels.

This is a bit hard to detect, and the most reliable way to find issues like this is to compile the kernel for both a 32-bit target and a 64-bit target (on x86, just turn CONFIG_64BIT on/off) to see all the compile-time errors and warnings.

Arnd