Re: [PATCH] time: Fix sign bug in ntp mult overflow warning
Xunlei, On Tue, Dec 02, 2014 at 11:00:26PM +0800, Xunlei Pang wrote: > On 2 December 2014 at 17:32, Jeremiah Mahler wrote: > > John, > > > > On Mon, Nov 24, 2014 at 08:35:45PM -0800, John Stultz wrote: > >> In commit 6067dc5a8c2b ("time: Avoid possible NTP adjustment mult > >> @@ -1330,7 +1330,7 @@ static __always_inline void > >> timekeeping_apply_adjustment(struct timekeeper *tk, [...] > >>* > >>* XXX - TODO: Doc ntp_error calculation. > >>*/ > >> - if (tk->tkr.mult + mult_adj < mult_adj) { > >> + if ((mult_adj > 0) && (tk->tkr.mult + mult_adj < mult_adj)) { > >> /* NTP adjustment caused clocksource mult overflow */ > >> WARN_ON_ONCE(1); > >> return; > > > > This change does quiet the warning but I think it does so for the wrong > > reason. > > > > mult_adj is a signed number and tk->tkr.mult is an unsigned number. > > Adding the check that (mult_adj > 0) limits the test to only positive > > numbers. A positive number plus a positive number will never be less > > than either of the two positive numbers. The test is always false. > > Hi Jeremiah, > > The result of a positive number plus a positive number may overflow, > for example, u32 (0x_FFF0 + 0x20) will be 0x10, > that's what this patch is dealing with. > > Thanks, > Xunlei > > > > -- > > - Jeremiah Mahler Oh, got it. That makes sense now. Thanks :) -- - Jeremiah Mahler -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] time: Fix sign bug in ntp mult overflow warning
On 2 December 2014 at 17:32, Jeremiah Mahler wrote: > John, > > On Mon, Nov 24, 2014 at 08:35:45PM -0800, John Stultz wrote: >> In commit 6067dc5a8c2b ("time: Avoid possible NTP adjustment mult >> overflow") a new check was added to watch for adjustments that could >> cause a mult overflow. >> >> Unfortunately the check compares a signed with unsigned value and >> ignored the case where the adjustment was negative, which causes >> spurious warn-ons on some systems (and seems like it would result in >> problematic time adjustments there as well, due to the early >> return). >> >> Thus this patch adds a check to make sure the adjustment is positive >> before we check for an overflow, and resovles the issue in my >> testing. >> >> Cc: pang.xunlei >> Cc: Fengguang Wu >> Cc: Thomas Gleixner >> Cc: Ingo Molnar >> Reported-by: Fengguang Wu >> Debugged-by: pang.xunlei >> Signed-off-by: John Stultz >> --- >> kernel/time/timekeeping.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c >> index 29a7d67..2dc0646 100644 >> --- a/kernel/time/timekeeping.c >> +++ b/kernel/time/timekeeping.c >> @@ -1330,7 +1330,7 @@ static __always_inline void >> timekeeping_apply_adjustment(struct timekeeper *tk, >>* >>* XXX - TODO: Doc ntp_error calculation. >>*/ >> - if (tk->tkr.mult + mult_adj < mult_adj) { >> + if ((mult_adj > 0) && (tk->tkr.mult + mult_adj < mult_adj)) { >> /* NTP adjustment caused clocksource mult overflow */ >> WARN_ON_ONCE(1); >> return; > > This change does quiet the warning but I think it does so for the wrong > reason. > > mult_adj is a signed number and tk->tkr.mult is an unsigned number. > Adding the check that (mult_adj > 0) limits the test to only positive > numbers. A positive number plus a positive number will never be less > than either of the two positive numbers. The test is always false. Hi Jeremiah, The result of a positive number plus a positive number may overflow, for example, u32 (0x_FFF0 + 0x20) will be 0x10, that's what this patch is dealing with. Thanks, Xunlei > > -- > - Jeremiah Mahler -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] time: Fix sign bug in ntp mult overflow warning
John, On Mon, Nov 24, 2014 at 08:35:45PM -0800, John Stultz wrote: > In commit 6067dc5a8c2b ("time: Avoid possible NTP adjustment mult > overflow") a new check was added to watch for adjustments that could > cause a mult overflow. > > Unfortunately the check compares a signed with unsigned value and > ignored the case where the adjustment was negative, which causes > spurious warn-ons on some systems (and seems like it would result in > problematic time adjustments there as well, due to the early > return). > > Thus this patch adds a check to make sure the adjustment is positive > before we check for an overflow, and resovles the issue in my > testing. > > Cc: pang.xunlei > Cc: Fengguang Wu > Cc: Thomas Gleixner > Cc: Ingo Molnar > Reported-by: Fengguang Wu > Debugged-by: pang.xunlei > Signed-off-by: John Stultz > --- > kernel/time/timekeeping.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > index 29a7d67..2dc0646 100644 > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -1330,7 +1330,7 @@ static __always_inline void > timekeeping_apply_adjustment(struct timekeeper *tk, >* >* XXX - TODO: Doc ntp_error calculation. >*/ > - if (tk->tkr.mult + mult_adj < mult_adj) { > + if ((mult_adj > 0) && (tk->tkr.mult + mult_adj < mult_adj)) { > /* NTP adjustment caused clocksource mult overflow */ > WARN_ON_ONCE(1); > return; This change does quiet the warning but I think it does so for the wrong reason. mult_adj is a signed number and tk->tkr.mult is an unsigned number. Adding the check that (mult_adj > 0) limits the test to only positive numbers. A positive number plus a positive number will never be less than either of the two positive numbers. The test is always false. -- - Jeremiah Mahler -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] time: Fix sign bug in ntp mult overflow warning
John, On Mon, Nov 24, 2014 at 08:35:45PM -0800, John Stultz wrote: In commit 6067dc5a8c2b (time: Avoid possible NTP adjustment mult overflow) a new check was added to watch for adjustments that could cause a mult overflow. Unfortunately the check compares a signed with unsigned value and ignored the case where the adjustment was negative, which causes spurious warn-ons on some systems (and seems like it would result in problematic time adjustments there as well, due to the early return). Thus this patch adds a check to make sure the adjustment is positive before we check for an overflow, and resovles the issue in my testing. Cc: pang.xunlei pang.xun...@linaro.org Cc: Fengguang Wu fengguang...@intel.com Cc: Thomas Gleixner t...@linutronix.de Cc: Ingo Molnar mi...@kernel.org Reported-by: Fengguang Wu fengguang...@intel.com Debugged-by: pang.xunlei pang.xun...@linaro.org Signed-off-by: John Stultz john.stu...@linaro.org --- kernel/time/timekeeping.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 29a7d67..2dc0646 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1330,7 +1330,7 @@ static __always_inline void timekeeping_apply_adjustment(struct timekeeper *tk, * * XXX - TODO: Doc ntp_error calculation. */ - if (tk-tkr.mult + mult_adj mult_adj) { + if ((mult_adj 0) (tk-tkr.mult + mult_adj mult_adj)) { /* NTP adjustment caused clocksource mult overflow */ WARN_ON_ONCE(1); return; This change does quiet the warning but I think it does so for the wrong reason. mult_adj is a signed number and tk-tkr.mult is an unsigned number. Adding the check that (mult_adj 0) limits the test to only positive numbers. A positive number plus a positive number will never be less than either of the two positive numbers. The test is always false. -- - Jeremiah Mahler -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] time: Fix sign bug in ntp mult overflow warning
On 2 December 2014 at 17:32, Jeremiah Mahler jmmah...@gmail.com wrote: John, On Mon, Nov 24, 2014 at 08:35:45PM -0800, John Stultz wrote: In commit 6067dc5a8c2b (time: Avoid possible NTP adjustment mult overflow) a new check was added to watch for adjustments that could cause a mult overflow. Unfortunately the check compares a signed with unsigned value and ignored the case where the adjustment was negative, which causes spurious warn-ons on some systems (and seems like it would result in problematic time adjustments there as well, due to the early return). Thus this patch adds a check to make sure the adjustment is positive before we check for an overflow, and resovles the issue in my testing. Cc: pang.xunlei pang.xun...@linaro.org Cc: Fengguang Wu fengguang...@intel.com Cc: Thomas Gleixner t...@linutronix.de Cc: Ingo Molnar mi...@kernel.org Reported-by: Fengguang Wu fengguang...@intel.com Debugged-by: pang.xunlei pang.xun...@linaro.org Signed-off-by: John Stultz john.stu...@linaro.org --- kernel/time/timekeeping.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 29a7d67..2dc0646 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1330,7 +1330,7 @@ static __always_inline void timekeeping_apply_adjustment(struct timekeeper *tk, * * XXX - TODO: Doc ntp_error calculation. */ - if (tk-tkr.mult + mult_adj mult_adj) { + if ((mult_adj 0) (tk-tkr.mult + mult_adj mult_adj)) { /* NTP adjustment caused clocksource mult overflow */ WARN_ON_ONCE(1); return; This change does quiet the warning but I think it does so for the wrong reason. mult_adj is a signed number and tk-tkr.mult is an unsigned number. Adding the check that (mult_adj 0) limits the test to only positive numbers. A positive number plus a positive number will never be less than either of the two positive numbers. The test is always false. Hi Jeremiah, The result of a positive number plus a positive number may overflow, for example, u32 (0x_FFF0 + 0x20) will be 0x10, that's what this patch is dealing with. Thanks, Xunlei -- - Jeremiah Mahler -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] time: Fix sign bug in ntp mult overflow warning
Xunlei, On Tue, Dec 02, 2014 at 11:00:26PM +0800, Xunlei Pang wrote: On 2 December 2014 at 17:32, Jeremiah Mahler jmmah...@gmail.com wrote: John, On Mon, Nov 24, 2014 at 08:35:45PM -0800, John Stultz wrote: In commit 6067dc5a8c2b (time: Avoid possible NTP adjustment mult @@ -1330,7 +1330,7 @@ static __always_inline void timekeeping_apply_adjustment(struct timekeeper *tk, [...] * * XXX - TODO: Doc ntp_error calculation. */ - if (tk-tkr.mult + mult_adj mult_adj) { + if ((mult_adj 0) (tk-tkr.mult + mult_adj mult_adj)) { /* NTP adjustment caused clocksource mult overflow */ WARN_ON_ONCE(1); return; This change does quiet the warning but I think it does so for the wrong reason. mult_adj is a signed number and tk-tkr.mult is an unsigned number. Adding the check that (mult_adj 0) limits the test to only positive numbers. A positive number plus a positive number will never be less than either of the two positive numbers. The test is always false. Hi Jeremiah, The result of a positive number plus a positive number may overflow, for example, u32 (0x_FFF0 + 0x20) will be 0x10, that's what this patch is dealing with. Thanks, Xunlei -- - Jeremiah Mahler Oh, got it. That makes sense now. Thanks :) -- - Jeremiah Mahler -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH] time: Fix sign bug in ntp mult overflow warning
In commit 6067dc5a8c2b ("time: Avoid possible NTP adjustment mult overflow") a new check was added to watch for adjustments that could cause a mult overflow. Unfortunately the check compares a signed with unsigned value and ignored the case where the adjustment was negative, which causes spurious warn-ons on some systems (and seems like it would result in problematic time adjustments there as well, due to the early return). Thus this patch adds a check to make sure the adjustment is positive before we check for an overflow, and resovles the issue in my testing. Cc: pang.xunlei Cc: Fengguang Wu Cc: Thomas Gleixner Cc: Ingo Molnar Reported-by: Fengguang Wu Debugged-by: pang.xunlei Signed-off-by: John Stultz --- kernel/time/timekeeping.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 29a7d67..2dc0646 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1330,7 +1330,7 @@ static __always_inline void timekeeping_apply_adjustment(struct timekeeper *tk, * * XXX - TODO: Doc ntp_error calculation. */ - if (tk->tkr.mult + mult_adj < mult_adj) { + if ((mult_adj > 0) && (tk->tkr.mult + mult_adj < mult_adj)) { /* NTP adjustment caused clocksource mult overflow */ WARN_ON_ONCE(1); return; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH] time: Fix sign bug in ntp mult overflow warning
In commit 6067dc5a8c2b (time: Avoid possible NTP adjustment mult overflow) a new check was added to watch for adjustments that could cause a mult overflow. Unfortunately the check compares a signed with unsigned value and ignored the case where the adjustment was negative, which causes spurious warn-ons on some systems (and seems like it would result in problematic time adjustments there as well, due to the early return). Thus this patch adds a check to make sure the adjustment is positive before we check for an overflow, and resovles the issue in my testing. Cc: pang.xunlei pang.xun...@linaro.org Cc: Fengguang Wu fengguang...@intel.com Cc: Thomas Gleixner t...@linutronix.de Cc: Ingo Molnar mi...@kernel.org Reported-by: Fengguang Wu fengguang...@intel.com Debugged-by: pang.xunlei pang.xun...@linaro.org Signed-off-by: John Stultz john.stu...@linaro.org --- kernel/time/timekeeping.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 29a7d67..2dc0646 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1330,7 +1330,7 @@ static __always_inline void timekeeping_apply_adjustment(struct timekeeper *tk, * * XXX - TODO: Doc ntp_error calculation. */ - if (tk-tkr.mult + mult_adj mult_adj) { + if ((mult_adj 0) (tk-tkr.mult + mult_adj mult_adj)) { /* NTP adjustment caused clocksource mult overflow */ WARN_ON_ONCE(1); return; -- 1.9.1 -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/