[PATCH v3 1/3] powerpc/perf: fix preempt count underflow in fsl_emb_pmu_del

[Aboorva Devarajan]

fsl_emb_pmu_del() unconditionally calls put_cpu_var(cpu_hw_events) at
the 'out:' label, but only calls the matching get_cpu_var() after the
'i < 0' early-return check. When event->hw.idx is negative the
function jumps to 'out:' without having taken get_cpu_var(), and the
trailing put_cpu_var() then issues an unmatched preempt_enable(),
underflowing preempt_count.

On a CONFIG_PREEMPT=y kernel preempt_count would underflow and
eventually present as a 'scheduling while atomic' BUG.

Move put_cpu_var() to pair with get_cpu_var() so the percpu access is
correctly bracketed and the 'out:' label only handles perf_pmu_enable.

Fixes: a11106544f33 ("powerpc/perf: e500 support")
Reviewed-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
Signed-off-by: Aboorva Devarajan <aboorvad@xxxxxxxxxxxxx>
---
 arch/powerpc/perf/core-fsl-emb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/perf/core-fsl-emb.c b/arch/powerpc/perf/core-fsl-emb.c
index 7120ab20cbfe..02b5dd74c187 100644
--- a/arch/powerpc/perf/core-fsl-emb.c
+++ b/arch/powerpc/perf/core-fsl-emb.c
@@ -366,9 +366,10 @@ static void fsl_emb_pmu_del(struct perf_event *event, int flags)
 
 	cpuhw->n_events--;
 
+	put_cpu_var(cpu_hw_events);
+
  out:
 	perf_pmu_enable(event->pmu);
-	put_cpu_var(cpu_hw_events);
 }
 
 static void fsl_emb_pmu_start(struct perf_event *event, int ef_flags)
-- 
2.54.0