linux-kernel - [PATCH v0 1/2] perf: Copy parent's address filter offsets on clone

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Date:   Fri, 15 Feb 2019 13:56:54 +0200
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        jolsa@...hat.com,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mansour Alharthi <malharthi9@...ech.edu>
Subject: [PATCH v0 1/2] perf: Copy parent's address filter offsets on clone

When a child event is allocated in the inherit_event() path, the VMA
based filter offsets are not copied from the parent, even though the
address space mapping of the new task remains the same, which leads
to no trace for the new task until exec.

Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Fixes: 375637bc5249 ("perf/core: Introduce address range filtering")
Reported-by: Mansour Alharthi <malharthi9@...ech.edu>
---
 kernel/events/core.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5aeb4c74fb99..2d89efc0a3e0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1255,6 +1255,7 @@ static void put_ctx(struct perf_event_context *ctx)
  *	      perf_event_context::lock
  *	    perf_event::mmap_mutex
  *	    mmap_sem
+ *	      perf_addr_filters_head::lock
  *
  *    cpu_hotplug_lock
  *      pmus_lock
@@ -10312,6 +10313,20 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 			goto err_per_task;
 		}
 
+		/*
+		 * Clone the parent's vma offsets: they are valid until exec()
+		 * even if the mm is not shared with the parent.
+		 */
+		if (event->parent) {
+			struct perf_addr_filters_head *ifh = perf_event_addr_filters(event);
+
+			raw_spin_lock_irq(&ifh->lock);
+			memcpy(event->addr_filters_offs,
+			       event->parent->addr_filters_offs,
+			       pmu->nr_addr_filters * sizeof(unsigned long));
+			raw_spin_unlock_irq(&ifh->lock);
+		}
+
 		/* force hw sync on the address filters */
 		event->addr_filters_gen = 1;
 	}
-- 
2.20.1