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Date: Mon, 13 Oct 2014 08:56:02 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Arnaldo Carvalho de Melo <acme@...radead.org>,
Jiri Olsa <jolsa@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: [GIT PULL] perf fixes, leftover from v3.17
Linus,
Please pull the latest perf-urgent-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git perf-urgent-for-linus
# HEAD: 9c2b9d30e28559a78c9e431cdd7f2c6bf5a9ee67 perf: Fix perf bug in fork()
Two leftover fixes from the v3.17 cycle - these will be forwarded
to -stable as well, if they prove problem-free in wider testing
as well.
Thanks,
Ingo
------------------>
Peter Zijlstra (2):
perf: Fix unclone_ctx() vs. locking
perf: Fix perf bug in fork()
kernel/events/core.c | 58 ++++++++++++++++++++++++++++++----------------------
kernel/fork.c | 5 +++--
2 files changed, 37 insertions(+), 26 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index d640a8b4dcbc..658f232af04c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -902,13 +902,23 @@ static void put_ctx(struct perf_event_context *ctx)
}
}
-static void unclone_ctx(struct perf_event_context *ctx)
+/*
+ * This must be done under the ctx->lock, such as to serialize against
+ * context_equiv(), therefore we cannot call put_ctx() since that might end up
+ * calling scheduler related locks and ctx->lock nests inside those.
+ */
+static __must_check struct perf_event_context *
+unclone_ctx(struct perf_event_context *ctx)
{
- if (ctx->parent_ctx) {
- put_ctx(ctx->parent_ctx);
+ struct perf_event_context *parent_ctx = ctx->parent_ctx;
+
+ lockdep_assert_held(&ctx->lock);
+
+ if (parent_ctx)
ctx->parent_ctx = NULL;
- }
ctx->generation++;
+
+ return parent_ctx;
}
static u32 perf_event_pid(struct perf_event *event, struct task_struct *p)
@@ -2210,6 +2220,9 @@ static void ctx_sched_out(struct perf_event_context *ctx,
static int context_equiv(struct perf_event_context *ctx1,
struct perf_event_context *ctx2)
{
+ lockdep_assert_held(&ctx1->lock);
+ lockdep_assert_held(&ctx2->lock);
+
/* Pinning disables the swap optimization */
if (ctx1->pin_count || ctx2->pin_count)
return 0;
@@ -2943,6 +2956,7 @@ static int event_enable_on_exec(struct perf_event *event,
*/
static void perf_event_enable_on_exec(struct perf_event_context *ctx)
{
+ struct perf_event_context *clone_ctx = NULL;
struct perf_event *event;
unsigned long flags;
int enabled = 0;
@@ -2974,7 +2988,7 @@ static void perf_event_enable_on_exec(struct perf_event_context *ctx)
* Unclone this context if we enabled any event.
*/
if (enabled)
- unclone_ctx(ctx);
+ clone_ctx = unclone_ctx(ctx);
raw_spin_unlock(&ctx->lock);
@@ -2984,6 +2998,9 @@ static void perf_event_enable_on_exec(struct perf_event_context *ctx)
perf_event_context_sched_in(ctx, ctx->task);
out:
local_irq_restore(flags);
+
+ if (clone_ctx)
+ put_ctx(clone_ctx);
}
void perf_event_exec(void)
@@ -3135,7 +3152,7 @@ find_lively_task_by_vpid(pid_t vpid)
static struct perf_event_context *
find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
{
- struct perf_event_context *ctx;
+ struct perf_event_context *ctx, *clone_ctx = NULL;
struct perf_cpu_context *cpuctx;
unsigned long flags;
int ctxn, err;
@@ -3169,9 +3186,12 @@ find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
retry:
ctx = perf_lock_task_context(task, ctxn, &flags);
if (ctx) {
- unclone_ctx(ctx);
+ clone_ctx = unclone_ctx(ctx);
++ctx->pin_count;
raw_spin_unlock_irqrestore(&ctx->lock, flags);
+
+ if (clone_ctx)
+ put_ctx(clone_ctx);
} else {
ctx = alloc_perf_context(pmu, task);
err = -ENOMEM;
@@ -7523,7 +7543,7 @@ __perf_event_exit_task(struct perf_event *child_event,
static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
{
struct perf_event *child_event, *next;
- struct perf_event_context *child_ctx, *parent_ctx;
+ struct perf_event_context *child_ctx, *clone_ctx = NULL;
unsigned long flags;
if (likely(!child->perf_event_ctxp[ctxn])) {
@@ -7550,28 +7570,16 @@ static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
child->perf_event_ctxp[ctxn] = NULL;
/*
- * In order to avoid freeing: child_ctx->parent_ctx->task
- * under perf_event_context::lock, grab another reference.
- */
- parent_ctx = child_ctx->parent_ctx;
- if (parent_ctx)
- get_ctx(parent_ctx);
-
- /*
* If this context is a clone; unclone it so it can't get
* swapped to another process while we're removing all
* the events from it.
*/
- unclone_ctx(child_ctx);
+ clone_ctx = unclone_ctx(child_ctx);
update_context_time(child_ctx);
raw_spin_unlock_irqrestore(&child_ctx->lock, flags);
- /*
- * Now that we no longer hold perf_event_context::lock, drop
- * our extra child_ctx->parent_ctx reference.
- */
- if (parent_ctx)
- put_ctx(parent_ctx);
+ if (clone_ctx)
+ put_ctx(clone_ctx);
/*
* Report the task dead after unscheduling the events so that we
@@ -7948,8 +7956,10 @@ int perf_event_init_task(struct task_struct *child)
for_each_task_context_nr(ctxn) {
ret = perf_event_init_context(child, ctxn);
- if (ret)
+ if (ret) {
+ perf_event_free_task(child);
return ret;
+ }
}
return 0;
diff --git a/kernel/fork.c b/kernel/fork.c
index 0cf9cdb6e491..a91e47d86de2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1360,7 +1360,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
goto bad_fork_cleanup_policy;
retval = audit_alloc(p);
if (retval)
- goto bad_fork_cleanup_policy;
+ goto bad_fork_cleanup_perf;
/* copy all the process information */
shm_init_task(p);
retval = copy_semundo(clone_flags, p);
@@ -1566,8 +1566,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
exit_sem(p);
bad_fork_cleanup_audit:
audit_free(p);
-bad_fork_cleanup_policy:
+bad_fork_cleanup_perf:
perf_event_free_task(p);
+bad_fork_cleanup_policy:
#ifdef CONFIG_NUMA
mpol_put(p->mempolicy);
bad_fork_cleanup_threadgroup_lock:
--
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