From: Russell Currey Date: Wed, 23 Aug 2023 05:53:17 +0000 (+1000) Subject: powerpc/pseries: Rework lppaca_shared_proc() to avoid DEBUG_PREEMPT X-Git-Tag: v6.6.7~2033^2~13 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=eac030b22ea12cdfcbb2e941c21c03964403c63f;p=platform%2Fkernel%2Flinux-starfive.git powerpc/pseries: Rework lppaca_shared_proc() to avoid DEBUG_PREEMPT lppaca_shared_proc() takes a pointer to the lppaca which is typically accessed through get_lppaca(). With DEBUG_PREEMPT enabled, this leads to checking if preemption is enabled, for example: BUG: using smp_processor_id() in preemptible [00000000] code: grep/10693 caller is lparcfg_data+0x408/0x19a0 CPU: 4 PID: 10693 Comm: grep Not tainted 6.5.0-rc3 #2 Call Trace: dump_stack_lvl+0x154/0x200 (unreliable) check_preemption_disabled+0x214/0x220 lparcfg_data+0x408/0x19a0 ... This isn't actually a problem however, as it does not matter which lppaca is accessed, the shared proc state will be the same. vcpudispatch_stats_procfs_init() already works around this by disabling preemption, but the lparcfg code does not, erroring any time /proc/powerpc/lparcfg is accessed with DEBUG_PREEMPT enabled. Instead of disabling preemption on the caller side, rework lppaca_shared_proc() to not take a pointer and instead directly access the lppaca, bypassing any potential preemption checks. Fixes: f13c13a00512 ("powerpc: Stop using non-architected shared_proc field in lppaca") Signed-off-by: Russell Currey [mpe: Rework to avoid needing a definition in paca.h and lppaca.h] Signed-off-by: Michael Ellerman Link: https://msgid.link/20230823055317.751786-4-mpe@ellerman.id.au --- diff --git a/arch/powerpc/include/asm/lppaca.h b/arch/powerpc/include/asm/lppaca.h index b6a63fa..61ec244 100644 --- a/arch/powerpc/include/asm/lppaca.h +++ b/arch/powerpc/include/asm/lppaca.h @@ -23,6 +23,7 @@ #include #include #include +#include /* * The lppaca is the "virtual processor area" registered with the hypervisor, @@ -105,14 +106,20 @@ struct lppaca { */ #define LPPACA_OLD_SHARED_PROC 2 -static inline bool lppaca_shared_proc(struct lppaca *l) +#ifdef CONFIG_PPC_PSERIES +/* + * All CPUs should have the same shared proc value, so directly access the PACA + * to avoid false positives from DEBUG_PREEMPT. + */ +static inline bool lppaca_shared_proc(void) { + struct lppaca *l = local_paca->lppaca_ptr; + if (!firmware_has_feature(FW_FEATURE_SPLPAR)) return false; return !!(l->__old_status & LPPACA_OLD_SHARED_PROC); } -#ifdef CONFIG_PPC_PSERIES #define get_lppaca() (get_paca()->lppaca_ptr) #endif diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c index 27fb656..f2cb621 100644 --- a/arch/powerpc/platforms/pseries/lpar.c +++ b/arch/powerpc/platforms/pseries/lpar.c @@ -640,16 +640,8 @@ static const struct proc_ops vcpudispatch_stats_freq_proc_ops = { static int __init vcpudispatch_stats_procfs_init(void) { - /* - * Avoid smp_processor_id while preemptible. All CPUs should have - * the same value for lppaca_shared_proc. - */ - preempt_disable(); - if (!lppaca_shared_proc(get_lppaca())) { - preempt_enable(); + if (!lppaca_shared_proc()) return 0; - } - preempt_enable(); if (!proc_create("powerpc/vcpudispatch_stats", 0600, NULL, &vcpudispatch_stats_proc_ops)) diff --git a/arch/powerpc/platforms/pseries/lparcfg.c b/arch/powerpc/platforms/pseries/lparcfg.c index 8acc705..1c151d7 100644 --- a/arch/powerpc/platforms/pseries/lparcfg.c +++ b/arch/powerpc/platforms/pseries/lparcfg.c @@ -206,7 +206,7 @@ static void parse_ppp_data(struct seq_file *m) ppp_data.active_system_procs); /* pool related entries are appropriate for shared configs */ - if (lppaca_shared_proc(get_lppaca())) { + if (lppaca_shared_proc()) { unsigned long pool_idle_time, pool_procs; seq_printf(m, "pool=%d\n", ppp_data.pool_num); @@ -560,7 +560,7 @@ static int pseries_lparcfg_data(struct seq_file *m, void *v) partition_potential_processors); seq_printf(m, "shared_processor_mode=%d\n", - lppaca_shared_proc(get_lppaca())); + lppaca_shared_proc()); #ifdef CONFIG_PPC_64S_HASH_MMU if (!radix_enabled()) diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c index bb0a9ae..ecea85c 100644 --- a/arch/powerpc/platforms/pseries/setup.c +++ b/arch/powerpc/platforms/pseries/setup.c @@ -849,7 +849,7 @@ static void __init pSeries_setup_arch(void) if (firmware_has_feature(FW_FEATURE_LPAR)) { vpa_init(boot_cpuid); - if (lppaca_shared_proc(get_lppaca())) { + if (lppaca_shared_proc()) { static_branch_enable(&shared_processor); pv_spinlocks_init(); #ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c index a7d33f3..14db9b7 100644 --- a/drivers/cpuidle/cpuidle-pseries.c +++ b/drivers/cpuidle/cpuidle-pseries.c @@ -414,13 +414,7 @@ static int __init pseries_idle_probe(void) return -ENODEV; if (firmware_has_feature(FW_FEATURE_SPLPAR)) { - /* - * Use local_paca instead of get_lppaca() since - * preemption is not disabled, and it is not required in - * fact, since lppaca_ptr does not need to be the value - * associated to the current CPU, it can be from any CPU. - */ - if (lppaca_shared_proc(local_paca->lppaca_ptr)) { + if (lppaca_shared_proc()) { cpuidle_state_table = shared_states; max_idle_state = ARRAY_SIZE(shared_states); } else {