On Fri, 23 Aug 2024, 陈玉凡 wrote:
> 在 2024/8/23 1:08, Mikulas Patocka 写道:
> >
> > On Thu, 22 Aug 2024, Chen Yufan wrote:
> >
> >> Use time_after_eq macro instead of opening it for readability.
> >>
> >> Signed-off-by: Chen Yufan <chenyufan@xxxxxxxx>
> >> ---
> >> drivers/md/dm-writecache.c | 5 +++--
> >> 1 file changed, 3 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
> >> index 7ce8847b3..548d4d37e 100644
> >> --- a/drivers/md/dm-writecache.c
> >> +++ b/drivers/md/dm-writecache.c
> >> @@ -16,6 +16,7 @@
> >> #include <linux/pfn_t.h>
> >> #include <linux/libnvdimm.h>
> >> #include <linux/delay.h>
> >> +#include <linux/jiffies.h>
> >> #include "dm-io-tracker.h"
> >>
> >> #define DM_MSG_PREFIX "writecache"
> >> @@ -1994,8 +1995,8 @@ static void writecache_writeback(struct work_struct *work)
> >> while (!list_empty(&wc->lru) &&
> >> (wc->writeback_all ||
> >> wc->freelist_size + wc->writeback_size <= wc->freelist_low_watermark ||
> >> - (jiffies - container_of(wc->lru.prev, struct wc_entry, lru)->age >=
> >> - wc->max_age - wc->max_age / MAX_AGE_DIV))) {
> >> + (time_after_eq(jiffies, container_of(wc->lru.prev, struct wc_entry, lru)->age +
> >> + (wc->max_age - wc->max_age / MAX_AGE_DIV))))) {
> >>
> >> n_walked++;
> >> if (unlikely(n_walked > WRITEBACK_LATENCY) &&
> >> --
> >> 2.39.0
> > I'm not sure about this. The old and new code is not really equivalent.
> >
> > Mikulas
>
> The code here is susceptible to overflow issues, and the time_*() macros
> can handle this.
>
> Chen
So, describe some case (i.e. the values of jiffies,
container_of(wc->lru.prev, struct wc_entry, lru)->age and wc->max_age)
where the old code misbehaves and the new code doesn't.
If we want to fix a bug, we need to know what the bug actually is.
Mikulas
