On Thursday, June 01, 2017 01:08:16 AM Jongman Heo wrote: > > > >--------- Original Message --------- > >Sender : Rafael J. Wysocki <[email protected]> > >Date : 2017-06-01 08:58 (GMT+9) > >Title : Re: FW: [4.12 regression] "cpufreq: intel_pstate: Active mode > >P-state limits rework" > > > >On Monday, May 29, 2017 02:18:52 AM Jongman Heo wrote: > >> > >> Hi, > >> > >> FYI, 4.12-rc3 still has this issue. > >> > >> > >> --------- Original Message --------- > >> Sender : 허종만 <[email protected]> > >> Date : 2017-05-16 13:25 (GMT+9) > >> Title : [4.12 regression] "cpufreq: intel_pstate: Active mode P-state > >> limits rework" > >> > >> > >> Hi, > >> > >> With 4.12-rc1 (Linus git), booting fails due to kernel panic, at > >> intel_pstate_register_driver+0x56/0x110. > >> I can't copy the whole trace from the graphic console, it looks like below. > >> > >> Call Trace: > >> intel_pstate_init > >> intel_pstate_setup > >> do_one_initcall > >> set_debug_rodata > >> kernel_init_freeable > >> rest_init > >> kernel_init > >> ret_from_fork > >> Code: ... > >> RIP: intel_pstate_register_driver+0x56/0x110 RSP: ffffa3a98000bd80 > >> ... > > > >I guess this is a division by 0 due to the unmet assumption that the > >denominator > >in min_perf_pct_min() will always be nonzero. > > > >If this guess is correct, the patch below should help, so can you please > >test it? > > > >Thanks, > >Rafael > > > > > >--- > > drivers/cpufreq/intel_pstate.c | 5 +++-- > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > >Index: linux-pm/drivers/cpufreq/intel_pstate.c > >=================================================================== > >--- linux-pm.orig/drivers/cpufreq/intel_pstate.c > >+++ linux-pm/drivers/cpufreq/intel_pstate.c > >@@ -571,9 +571,10 @@ static inline void update_turbo_state(vo > > static int min_perf_pct_min(void) > > { > > struct cpudata *cpu = all_cpu_data[0]; > >+ int turbo_pstate = cpu->pstate.turbo_pstate; > > > >- return DIV_ROUND_UP(cpu->pstate.min_pstate * 100, > >- cpu->pstate.turbo_pstate); > >+ return turbo_pstate ? > >+ DIV_ROUND_UP(cpu->pstate.min_pstate * 100, turbo_pstate) : > >0; > > } > > > > static s16 intel_pstate_get_epb(struct cpudata *cpu_data) > > > > > > > > Hi, > > Your patch fixes the issue.
OK, thanks for the confirmation. Here it goes again with a changelog and all. --- From: Rafael J. Wysocki <[email protected]> Subject: [PATCH] cpufreq: intel_pstate: Avoid division by 0 in min_perf_pct_min() Commit c5a2ee7dde89 (cpufreq: intel_pstate: Active mode P-state limits rework) incorrectly assumed that pstate.turbo_pstate will always be nonzero for CPU0 in min_perf_pct_min() if cpufreq_register_driver() has succeeded which may not be the case in virtualized environments. If that is not the case, it leads to an early crash on boot in intel_pstate_register_driver(), so add a sanity check to min_perf_pct_min() to prevent the crash from happening. Fixes: c5a2ee7dde89 (cpufreq: intel_pstate: Active mode P-state limits rework) Reported-and-tested-by: Jongman Heo <[email protected]> Signed-off-by: Rafael J. Wysocki <[email protected]> --- drivers/cpufreq/intel_pstate.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) Index: linux-pm/drivers/cpufreq/intel_pstate.c =================================================================== --- linux-pm.orig/drivers/cpufreq/intel_pstate.c +++ linux-pm/drivers/cpufreq/intel_pstate.c @@ -571,9 +571,10 @@ static inline void update_turbo_state(vo static int min_perf_pct_min(void) { struct cpudata *cpu = all_cpu_data[0]; + int turbo_pstate = cpu->pstate.turbo_pstate; - return DIV_ROUND_UP(cpu->pstate.min_pstate * 100, - cpu->pstate.turbo_pstate); + return turbo_pstate ? + DIV_ROUND_UP(cpu->pstate.min_pstate * 100, turbo_pstate) : 0; } static s16 intel_pstate_get_epb(struct cpudata *cpu_data)
