powerpc/perf_counters: Reduce stack usage of power_check_constraints

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>
Cc: <stable@kernel.org)
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 32 insertions, 23 deletions

diff --git a/arch/powerpc/kernel/perf_counter.c b/arch/powerpc/kernel/perf_counter.c
index ccd6b2135642..7ceefaf3a7f5 100644
--- 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);
 
@@ -239,13 +242,11 @@ static void write_pmc(int idx, unsigned long val)
  * 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;
@@ -260,21 +261,23 @@ static int power_check_constraints(u64 event[], unsigned int cflags[],
                 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 */
@@ -285,10 +288,11 @@ static int power_check_constraints(u64 event[], unsigned int cflags[],
         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 */
@@ -307,11 +311,11 @@ static int power_check_constraints(u64 event[], unsigned int cflags[],
                  * 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]) {
@@ -333,7 +337,7 @@ static int power_check_constraints(u64 event[], unsigned int cflags[],
                         svalues[i] = value;
                         smasks[i] = mask;
                         value = nv;
-                        mask |= amasks[i][j];
+                        mask |= cpuhw->amasks[i][j];
                         ++i;
                         j = -1;
                 }
@@ -341,7 +345,7 @@ static int power_check_constraints(u64 event[], unsigned int cflags[],
 
         /* 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;
 }
 
@@ -745,7 +749,7 @@ int hw_perf_group_sched_in(struct perf_counter *group_leader,
                 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;
@@ -800,7 +804,7 @@ static int power_pmu_enable(struct perf_counter *counter)
         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];
@@ -1005,6 +1009,7 @@ const struct pmu *hw_perf_counter_init(struct perf_counter *counter)
         unsigned int cflags[MAX_HWCOUNTERS];
         int n;
         int err;
+        struct cpu_hw_counters *cpuhw;
 
         if (!ppmu)
                 return ERR_PTR(-ENXIO);
@@ -1083,7 +1088,11 @@ const struct pmu *hw_perf_counter_init(struct perf_counter *counter)
         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];