From 2565e42539b120b81a68a58da961ce5d1e34eac8 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 4 Nov 2024 14:39:11 +0100 Subject: perf/core: Fix pmus_lock vs. pmus_srcu ordering Commit a63fbed776c7 ("perf/tracing/cpuhotplug: Fix locking order") placed pmus_lock inside pmus_srcu, this makes perf_pmu_unregister() trip lockdep. Move the locking about such that only pmu_idr and pmus (list) are modified while holding pmus_lock. This avoids doing synchronize_srcu() while holding pmus_lock and all is well again. Fixes: a63fbed776c7 ("perf/tracing/cpuhotplug: Fix locking order") Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20241104135517.679556858@infradead.org --- kernel/events/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/events/core.c b/kernel/events/core.c index 6364319e2f88..11793d690cbb 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -11939,6 +11939,8 @@ void perf_pmu_unregister(struct pmu *pmu) { mutex_lock(&pmus_lock); list_del_rcu(&pmu->entry); + idr_remove(&pmu_idr, pmu->type); + mutex_unlock(&pmus_lock); /* * We dereference the pmu list under both SRCU and regular RCU, so @@ -11948,7 +11950,6 @@ void perf_pmu_unregister(struct pmu *pmu) synchronize_rcu(); free_percpu(pmu->pmu_disable_count); - idr_remove(&pmu_idr, pmu->type); if (pmu_bus_running && pmu->dev && pmu->dev != PMU_NULL_DEV) { if (pmu->nr_addr_filters) device_remove_file(pmu->dev, &dev_attr_nr_addr_filters); @@ -11956,7 +11957,6 @@ void perf_pmu_unregister(struct pmu *pmu) put_device(pmu->dev); } free_pmu_context(pmu); - mutex_unlock(&pmus_lock); } EXPORT_SYMBOL_GPL(perf_pmu_unregister); -- cgit v1.2.3 From 003659fec9f6d8c04738cb74b5384398ae8a7e88 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 4 Nov 2024 14:39:12 +0100 Subject: perf/core: Fix perf_pmu_register() vs. perf_init_event() There is a fairly obvious race between perf_init_event() doing idr_find() and perf_pmu_register() doing idr_alloc() with an incompletely initialized PMU pointer. Avoid by doing idr_alloc() on a NULL pointer to register the id, and swizzling the real struct pmu pointer at the end using idr_replace(). Also making sure to not set struct pmu members after publishing the struct pmu, duh. [ introduce idr_cmpxchg() in order to better handle the idr_replace() error case -- if it were to return an unexpected pointer, it will already have replaced the value and there is no going back. ] Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20241104135517.858805880@infradead.org --- kernel/events/core.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/events/core.c b/kernel/events/core.c index 11793d690cbb..823aa0824916 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -11830,6 +11830,21 @@ free_dev: static struct lock_class_key cpuctx_mutex; static struct lock_class_key cpuctx_lock; +static bool idr_cmpxchg(struct idr *idr, unsigned long id, void *old, void *new) +{ + void *tmp, *val = idr_find(idr, id); + + if (val != old) + return false; + + tmp = idr_replace(idr, new, id); + if (IS_ERR(tmp)) + return false; + + WARN_ON_ONCE(tmp != val); + return true; +} + int perf_pmu_register(struct pmu *pmu, const char *name, int type) { int cpu, ret, max = PERF_TYPE_MAX; @@ -11856,7 +11871,7 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type) if (type >= 0) max = type; - ret = idr_alloc(&pmu_idr, pmu, max, 0, GFP_KERNEL); + ret = idr_alloc(&pmu_idr, NULL, max, 0, GFP_KERNEL); if (ret < 0) goto free_pdc; @@ -11864,6 +11879,7 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type) type = ret; pmu->type = type; + atomic_set(&pmu->exclusive_cnt, 0); if (pmu_bus_running && !pmu->dev) { ret = pmu_dev_alloc(pmu); @@ -11912,14 +11928,22 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type) if (!pmu->event_idx) pmu->event_idx = perf_event_idx_default; + /* + * Now that the PMU is complete, make it visible to perf_try_init_event(). + */ + if (!idr_cmpxchg(&pmu_idr, pmu->type, NULL, pmu)) + goto free_context; list_add_rcu(&pmu->entry, &pmus); - atomic_set(&pmu->exclusive_cnt, 0); + ret = 0; unlock: mutex_unlock(&pmus_lock); return ret; +free_context: + free_percpu(pmu->cpu_pmu_context); + free_dev: if (pmu->dev && pmu->dev != PMU_NULL_DEV) { device_del(pmu->dev); -- cgit v1.2.3