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FAILED: patch "[PATCH] perf/x86/lbr: Remove cpuc->lbr_xsave allocation from atomic" failed to apply to 5.10-stable tree

PATCH [email protected] 1 participant 1 message May 24, 2021

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The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 488e13a489e9707a7e81e1991fdd1f20c0f04689 Mon Sep 17 00:00:00 2001
From: Like Xu <[email protected]>
Date: Fri, 30 Apr 2021 13:22:47 +0800
Subject: [PATCH] perf/x86/lbr: Remove cpuc->lbr_xsave allocation from atomic
context

If the kernel is compiled with the CONFIG_LOCKDEP option, the conditional might_sleep_if() deep in kmem_cache_alloc() will generate the following trace, and potentially cause a deadlock when another LBR event is added:

[] BUG: sleeping function called from invalid context at include/linux/sched/mm.h:196 [] Call Trace:

  []  kmem_cache_alloc+0x36/0x250
  []  intel_pmu_lbr_add+0x152/0x170
  []  x86_pmu_add+0x83/0xd0

Make it symmetric with the release_lbr_buffers() call and mirror the existing DS buffers.

Fixes c085fb8774 ("perf/x86/intel/lbr: Support XSAVES for arch LBR read")
Signed-off-by Like Xu <[email protected]>
[peterz: simplified]
Signed-off-by Peter Zijlstra (Intel) <[email protected]>
Tested-by Kan Liang <[email protected]>
Link https://lkml.kernel.org/r/[email protected] open here
arch/x86/events/core.c +4 -2
index 8e509325c2c3..8f71dd72ef95 100644
@@ -396,10 +396,12 @@ int x86_reserve_hardware(void)
 	if (!atomic_inc_not_zero(&pmc_refcount)) {
 		mutex_lock(&pmc_reserve_mutex);
 		if (atomic_read(&pmc_refcount) == 0) {
-			if (!reserve_pmc_hardware())
+			if (!reserve_pmc_hardware()) {
 				err = -EBUSY;
-			else
+			} else {
 				reserve_ds_buffers();
+				reserve_lbr_buffers();
+			}
 		}
 		if (!err)
 			atomic_inc(&pmc_refcount);
arch/x86/events/intel/lbr.c +20 -6
index 76dbab6ac9fb..4409d2cccfda 100644
@@ -658,7 +658,6 @@ static inline bool branch_user_callstack(unsigned br_sel)
 
 void intel_pmu_lbr_add(struct perf_event *event)
 {
-	struct kmem_cache *kmem_cache = event->pmu->task_ctx_cache;
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 
 	if (!x86_pmu.lbr_nr)

@@ -696,11 +695,6 @@ void intel_pmu_lbr_add(struct perf_event *event)
 	perf_sched_cb_inc(event->ctx->pmu);
 	if (!cpuc->lbr_users++ && !event->total_time_running)
 		intel_pmu_lbr_reset();
-
-	if (static_cpu_has(X86_FEATURE_ARCH_LBR) &&
-	    kmem_cache && !cpuc->lbr_xsave &&
-	    (cpuc->lbr_users != cpuc->lbr_pebs_users))
-		cpuc->lbr_xsave = kmem_cache_alloc(kmem_cache, GFP_KERNEL);
 }
 
 void release_lbr_buffers(void)

@@ -722,6 +716,26 @@ void release_lbr_buffers(void)
 	}
 }
 
+void reserve_lbr_buffers(void)
+{
+	struct kmem_cache *kmem_cache;
+	struct cpu_hw_events *cpuc;
+	int cpu;
+
+	if (!static_cpu_has(X86_FEATURE_ARCH_LBR))
+		return;
+
+	for_each_possible_cpu(cpu) {
+		cpuc = per_cpu_ptr(&cpu_hw_events, cpu);
+		kmem_cache = x86_get_pmu(cpu)->task_ctx_cache;
+		if (!kmem_cache || cpuc->lbr_xsave)
+			continue;
+
+		cpuc->lbr_xsave = kmem_cache_alloc_node(kmem_cache, GFP_KERNEL,
+							cpu_to_node(cpu));
+	}
+}
+
 void intel_pmu_lbr_del(struct perf_event *event)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
arch/x86/events/perf_event.h +6 -0
index 27fa85e7d4fd..ad87cb36f7c8 100644
@@ -1244,6 +1244,8 @@ void reserve_ds_buffers(void);
 
 void release_lbr_buffers(void);
 
+void reserve_lbr_buffers(void);
+
 extern struct event_constraint bts_constraint;
 extern struct event_constraint vlbr_constraint;
 

@@ -1393,6 +1395,10 @@ static inline void release_lbr_buffers(void)
 {
 }
 
+static inline void reserve_lbr_buffers(void)
+{
+}
+
 static inline int intel_pmu_init(void)
 {
 	return 0;