| Message ID | 20240822015416.3627-1-chenyufan@vivo.com (mailing list archive) |
|---|---|
| State | Rejected, archived |
| Delegated to: | Mikulas Patocka |
| Headers | show |
| Series | [v1] Device-mapper(LVM): Convert to use time_after_eq macro | expand |
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@vivo.com> > --- > 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
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@vivo.com> >> --- >> 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 >
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@vivo.com> > >> --- > >> 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
On Mon, 26 Aug 2024, 陈玉凡 wrote: > 在 2024/8/24 3:01, Mikulas Patocka 写道: > > > 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@vivo.com> > --- > 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 > > When jiffies increased beyond the maximum value of unsigned long, it > wraps around to zero, and the value of jiffies would be smaller than the > container_of(wc->lru.prev, struct wc_entry, lru)->age value despite > logically being larger. Eventurally, because of the wraparound, the > result of the condition would be wrong. > > Chen For example, if "jiffies" is 0x10 (because it wrapped around) and "container_of(wc->lru.prev, struct wc_entry, lru)->age" is 0xfffffff0, then the expression "jiffies - container_of(wc->lru.prev, struct wc_entry, lru)->age" would be 0x20. That is the correct value, I don't see any problem with this. Mikulas
On Thu, 29 Aug 2024, 陈玉凡 wrote: > When "jiffies" is 0x10 (because of wraparound) and > "container_of(wc->lru.prev, struct wc_entry, lru)->age" is 0x1(I'm not > sure if it can be such a small value), the result will change from a > large value to a small value. > > Chen So, the when you subtract the numbers, you get 0xf. There's nothing wrong with it. Mikulas
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) &&
Use time_after_eq macro instead of opening it for readability. Signed-off-by: Chen Yufan <chenyufan@vivo.com> --- drivers/md/dm-writecache.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)