diff options
Diffstat (limited to 'debian/patches-rt/0005-perf-Move-swevent_htable-recursion-into-task_struct.patch')
| -rw-r--r-- | debian/patches-rt/0005-perf-Move-swevent_htable-recursion-into-task_struct.patch | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/debian/patches-rt/0005-perf-Move-swevent_htable-recursion-into-task_struct.patch b/debian/patches-rt/0005-perf-Move-swevent_htable-recursion-into-task_struct.patch new file mode 100644 index 0000000000..5070c10a30 --- /dev/null +++ b/debian/patches-rt/0005-perf-Move-swevent_htable-recursion-into-task_struct.patch @@ -0,0 +1,121 @@ +From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Date: Thu, 4 Jul 2024 19:03:39 +0200 +Subject: [PATCH 5/7] perf: Move swevent_htable::recursion into task_struct. +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.10/older/patches-6.10.2-rt14.tar.xz + +The swevent_htable::recursion counter is used to avoid creating an +swevent while an event is processed to avoid recursion. The counter is +per-CPU and preemption must be disabled to have a stable counter. +perf_pending_task() disables preemption to access the counter and then +signal. This is problematic on PREEMPT_RT because sending a signal uses +a spinlock_t which must not be acquired in atomic on PREEMPT_RT because +it becomes a sleeping lock. + +The atomic context can be avoided by moving the counter into the +task_struct. There is a 4 byte hole between futex_state (usually always +on) and the following perf pointer (perf_event_ctxp). After the +recursion lost some weight it fits perfectly. + +Move swevent_htable::recursion into task_struct. + +Tested-by: Marco Elver <elver@google.com> +Link: https://lore.kernel.org/r/20240704170424.1466941-6-bigeasy@linutronix.de +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + include/linux/perf_event.h | 6 ------ + include/linux/sched.h | 7 +++++++ + kernel/events/core.c | 13 +++---------- + kernel/events/internal.h | 2 +- + 4 files changed, 11 insertions(+), 17 deletions(-) + +--- a/include/linux/perf_event.h ++++ b/include/linux/perf_event.h +@@ -970,12 +970,6 @@ struct perf_event_context { + local_t nr_pending; + }; + +-/* +- * Number of contexts where an event can trigger: +- * task, softirq, hardirq, nmi. +- */ +-#define PERF_NR_CONTEXTS 4 +- + struct perf_cpu_pmu_context { + struct perf_event_pmu_context epc; + struct perf_event_pmu_context *task_epc; +--- a/include/linux/sched.h ++++ b/include/linux/sched.h +@@ -734,6 +734,12 @@ enum perf_event_task_context { + perf_nr_task_contexts, + }; + ++/* ++ * Number of contexts where an event can trigger: ++ * task, softirq, hardirq, nmi. ++ */ ++#define PERF_NR_CONTEXTS 4 ++ + struct wake_q_node { + struct wake_q_node *next; + }; +@@ -1256,6 +1262,7 @@ struct task_struct { + unsigned int futex_state; + #endif + #ifdef CONFIG_PERF_EVENTS ++ u8 perf_recursion[PERF_NR_CONTEXTS]; + struct perf_event_context *perf_event_ctxp; + struct mutex perf_event_mutex; + struct list_head perf_event_list; +--- a/kernel/events/core.c ++++ b/kernel/events/core.c +@@ -9774,11 +9774,7 @@ struct swevent_htable { + struct swevent_hlist *swevent_hlist; + struct mutex hlist_mutex; + int hlist_refcount; +- +- /* Recursion avoidance in each contexts */ +- u8 recursion[PERF_NR_CONTEXTS]; + }; +- + static DEFINE_PER_CPU(struct swevent_htable, swevent_htable); + + /* +@@ -9976,17 +9972,13 @@ DEFINE_PER_CPU(struct pt_regs, __perf_re + + int perf_swevent_get_recursion_context(void) + { +- struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable); +- +- return get_recursion_context(swhash->recursion); ++ return get_recursion_context(current->perf_recursion); + } + EXPORT_SYMBOL_GPL(perf_swevent_get_recursion_context); + + void perf_swevent_put_recursion_context(int rctx) + { +- struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable); +- +- put_recursion_context(swhash->recursion, rctx); ++ put_recursion_context(current->perf_recursion, rctx); + } + + void ___perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr) +@@ -13653,6 +13645,7 @@ int perf_event_init_task(struct task_str + { + int ret; + ++ memset(child->perf_recursion, 0, sizeof(child->perf_recursion)); + child->perf_event_ctxp = NULL; + mutex_init(&child->perf_event_mutex); + INIT_LIST_HEAD(&child->perf_event_list); +--- a/kernel/events/internal.h ++++ b/kernel/events/internal.h +@@ -221,7 +221,7 @@ static inline int get_recursion_context( + return rctx; + } + +-static inline void put_recursion_context(u8 *recursion, int rctx) ++static inline void put_recursion_context(u8 *recursion, unsigned char rctx) + { + barrier(); + recursion[rctx]--; |