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Subject[patch 17/45] powerpc/perf_counters: Reduce stack usage of power_check_constraints
2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Paul Mackerras <paulus@samba.org>

commit e51ee31e8af22948dcc3b115978469b09c96c3fd upstream.

Michael Ellerman reported stack-frame size warnings being produced
for power_check_constraints(), which uses an 8*8 array of u64 and
two 8*8 arrays of unsigned long, which are currently allocated on the
stack, along with some other smaller variables. These arrays come
to 1.5kB on 64-bit or 1kB on 32-bit, which is a bit too much for the
stack.

This fixes the problem by putting these arrays in the existing
per-cpu cpu_hw_counters struct. This is OK because two of the call
sites have interrupts disabled already; for the third call site we
use get_cpu_var, which disables preemption, so we know we won't
get a context switch while we're in power_check_constraints().
Note that power_check_constraints() can be called during context
switch but is not called from interrupts.

Reported-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/powerpc/kernel/perf_counter.c | 55 +++++++++++++++++++++----------------
1 file changed, 32 insertions(+), 23 deletions(-)

--- a/arch/powerpc/kernel/perf_counter.c
+++ b/arch/powerpc/kernel/perf_counter.c
@@ -32,6 +32,9 @@ struct cpu_hw_counters {
unsigned long mmcr[3];
struct perf_counter *limited_counter[MAX_LIMITED_HWCOUNTERS];
u8 limited_hwidx[MAX_LIMITED_HWCOUNTERS];
+ u64 alternatives[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
+ unsigned long amasks[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
+ unsigned long avalues[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
};
DEFINE_PER_CPU(struct cpu_hw_counters, cpu_hw_counters);

@@ -245,13 +248,11 @@ static void write_pmc(int idx, unsigned
* and see if any combination of alternative codes is feasible.
* The feasible set is returned in event[].
*/
-static int power_check_constraints(u64 event[], unsigned int cflags[],
+static int power_check_constraints(struct cpu_hw_counters *cpuhw,
+ u64 event[], unsigned int cflags[],
int n_ev)
{
unsigned long mask, value, nv;
- u64 alternatives[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
- unsigned long amasks[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
- unsigned long avalues[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
unsigned long smasks[MAX_HWCOUNTERS], svalues[MAX_HWCOUNTERS];
int n_alt[MAX_HWCOUNTERS], choice[MAX_HWCOUNTERS];
int i, j;
@@ -266,21 +267,23 @@ static int power_check_constraints(u64 e
if ((cflags[i] & PPMU_LIMITED_PMC_REQD)
&& !ppmu->limited_pmc_event(event[i])) {
ppmu->get_alternatives(event[i], cflags[i],
- alternatives[i]);
- event[i] = alternatives[i][0];
+ cpuhw->alternatives[i]);
+ event[i] = cpuhw->alternatives[i][0];
}
- if (ppmu->get_constraint(event[i], &amasks[i][0],
- &avalues[i][0]))
+ if (ppmu->get_constraint(event[i], &cpuhw->amasks[i][0],
+ &cpuhw->avalues[i][0]))
return -1;
}
value = mask = 0;
for (i = 0; i < n_ev; ++i) {
- nv = (value | avalues[i][0]) + (value & avalues[i][0] & addf);
+ nv = (value | cpuhw->avalues[i][0]) +
+ (value & cpuhw->avalues[i][0] & addf);
if ((((nv + tadd) ^ value) & mask) != 0 ||
- (((nv + tadd) ^ avalues[i][0]) & amasks[i][0]) != 0)
+ (((nv + tadd) ^ cpuhw->avalues[i][0]) &
+ cpuhw->amasks[i][0]) != 0)
break;
value = nv;
- mask |= amasks[i][0];
+ mask |= cpuhw->amasks[i][0];
}
if (i == n_ev)
return 0; /* all OK */
@@ -291,10 +294,11 @@ static int power_check_constraints(u64 e
for (i = 0; i < n_ev; ++i) {
choice[i] = 0;
n_alt[i] = ppmu->get_alternatives(event[i], cflags[i],
- alternatives[i]);
+ cpuhw->alternatives[i]);
for (j = 1; j < n_alt[i]; ++j)
- ppmu->get_constraint(alternatives[i][j],
- &amasks[i][j], &avalues[i][j]);
+ ppmu->get_constraint(cpuhw->alternatives[i][j],
+ &cpuhw->amasks[i][j],
+ &cpuhw->avalues[i][j]);
}

/* enumerate all possibilities and see if any will work */
@@ -313,11 +317,11 @@ static int power_check_constraints(u64 e
* where k > j, will satisfy the constraints.
*/
while (++j < n_alt[i]) {
- nv = (value | avalues[i][j]) +
- (value & avalues[i][j] & addf);
+ nv = (value | cpuhw->avalues[i][j]) +
+ (value & cpuhw->avalues[i][j] & addf);
if ((((nv + tadd) ^ value) & mask) == 0 &&
- (((nv + tadd) ^ avalues[i][j])
- & amasks[i][j]) == 0)
+ (((nv + tadd) ^ cpuhw->avalues[i][j])
+ & cpuhw->amasks[i][j]) == 0)
break;
}
if (j >= n_alt[i]) {
@@ -339,7 +343,7 @@ static int power_check_constraints(u64 e
svalues[i] = value;
smasks[i] = mask;
value = nv;
- mask |= amasks[i][j];
+ mask |= cpuhw->amasks[i][j];
++i;
j = -1;
}
@@ -347,7 +351,7 @@ static int power_check_constraints(u64 e

/* OK, we have a feasible combination, tell the caller the solution */
for (i = 0; i < n_ev; ++i)
- event[i] = alternatives[i][choice[i]];
+ event[i] = cpuhw->alternatives[i][choice[i]];
return 0;
}

@@ -752,7 +756,7 @@ int hw_perf_group_sched_in(struct perf_c
return -EAGAIN;
if (check_excludes(cpuhw->counter, cpuhw->flags, n0, n))
return -EAGAIN;
- i = power_check_constraints(cpuhw->events, cpuhw->flags, n + n0);
+ i = power_check_constraints(cpuhw, cpuhw->events, cpuhw->flags, n + n0);
if (i < 0)
return -EAGAIN;
cpuhw->n_counters = n0 + n;
@@ -807,7 +811,7 @@ static int power_pmu_enable(struct perf_
cpuhw->flags[n0] = counter->hw.counter_base;
if (check_excludes(cpuhw->counter, cpuhw->flags, n0, 1))
goto out;
- if (power_check_constraints(cpuhw->events, cpuhw->flags, n0 + 1))
+ if (power_check_constraints(cpuhw, cpuhw->events, cpuhw->flags, n0 + 1))
goto out;

counter->hw.config = cpuhw->events[n0];
@@ -1012,6 +1016,7 @@ const struct pmu *hw_perf_counter_init(s
unsigned int cflags[MAX_HWCOUNTERS];
int n;
int err;
+ struct cpu_hw_counters *cpuhw;

if (!ppmu)
return ERR_PTR(-ENXIO);
@@ -1090,7 +1095,11 @@ const struct pmu *hw_perf_counter_init(s
cflags[n] = flags;
if (check_excludes(ctrs, cflags, n, 1))
return ERR_PTR(-EINVAL);
- if (power_check_constraints(events, cflags, n + 1))
+
+ cpuhw = &get_cpu_var(cpu_hw_counters);
+ err = power_check_constraints(cpuhw, events, cflags, n + 1);
+ put_cpu_var(cpu_hw_counters);
+ if (err)
return ERR_PTR(-EINVAL);

counter->hw.config = events[n];



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