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    Subject[PATCH 3.16 14/87] powerpc/perf: add missing put_cpu_var in power_pmu_event_init
    3.16.75-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jan Stancek <jstancek@redhat.com>

    commit 68de8867ea5d99127e836c23f6bccf4d44859623 upstream.

    One path in power_pmu_event_init() calls get_cpu_var(), but is
    missing matching call to put_cpu_var(), which causes preemption
    imbalance and crash in user-space:

    Page fault in user mode with in_atomic() = 1 mm = c000001fefa5a280
    NIP = 3fff9bf2cae0 MSR = 900000014280f032
    Oops: Weird page fault, sig: 11 [#23]
    SMP NR_CPUS=2048 NUMA PowerNV
    Modules linked in: <snip>
    CPU: 43 PID: 10285 Comm: a.out Tainted: G D 4.0.0-rc5+ #1
    task: c000001fe82c9200 ti: c000001fe835c000 task.ti: c000001fe835c000
    NIP: 00003fff9bf2cae0 LR: 00003fff9bee4898 CTR: 00003fff9bf2cae0
    REGS: c000001fe835fea0 TRAP: 0401 Tainted: G D (4.0.0-rc5+)
    MSR: 900000014280f032 <SF,HV,VEC,VSX,EE,PR,FP,ME,IR,DR,RI> CR: 22000028 XER: 00000000
    CFAR: 00003fff9bee4894 SOFTE: 1
    GPR00: 00003fff9bee494c 00003fffe01c2ee0 00003fff9c084410 0000000010020068
    GPR04: 0000000000000000 0000000000000002 0000000000000008 0000000000000001
    GPR08: 0000000000000001 00003fff9c074a30 00003fff9bf2cae0 00003fff9bf2cd70
    GPR12: 0000000052000022 00003fff9c10b700
    NIP [00003fff9bf2cae0] 0x3fff9bf2cae0
    LR [00003fff9bee4898] 0x3fff9bee4898
    Call Trace:
    ---[ end trace 5d3d952b5d4185d4 ]---

    BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:41
    in_atomic(): 1, irqs_disabled(): 0, pid: 10285, name: a.out
    INFO: lockdep is turned off.
    CPU: 43 PID: 10285 Comm: a.out Tainted: G D 4.0.0-rc5+ #1
    Call Trace:
    [c000001fe835f990] [c00000000089c014] .dump_stack+0x98/0xd4 (unreliable)
    [c000001fe835fa10] [c0000000000e4138] .___might_sleep+0x1d8/0x2e0
    [c000001fe835faa0] [c000000000888da8] .down_read+0x38/0x110
    [c000001fe835fb30] [c0000000000bf2f4] .exit_signals+0x24/0x160
    [c000001fe835fbc0] [c0000000000abde0] .do_exit+0xd0/0xe70
    [c000001fe835fcb0] [c00000000001f4c4] .die+0x304/0x450
    [c000001fe835fd60] [c00000000088e1f4] .do_page_fault+0x2d4/0x900
    [c000001fe835fe30] [c000000000008664] handle_page_fault+0x10/0x30
    note: a.out[10285] exited with preempt_count 1

    Reproducer:
    #include <stdio.h>
    #include <unistd.h>
    #include <syscall.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <linux/perf_event.h>
    #include <linux/hw_breakpoint.h>

    static struct perf_event_attr event = {
    .type = PERF_TYPE_RAW,
    .size = sizeof(struct perf_event_attr),
    .sample_type = PERF_SAMPLE_BRANCH_STACK,
    .branch_sample_type = PERF_SAMPLE_BRANCH_ANY_RETURN,
    };

    int main()
    {
    syscall(__NR_perf_event_open, &event, 0, -1, -1, 0);
    }

    Signed-off-by: Jan Stancek <jstancek@redhat.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    arch/powerpc/perf/core-book3s.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/arch/powerpc/perf/core-book3s.c
    +++ b/arch/powerpc/perf/core-book3s.c
    @@ -1825,8 +1825,10 @@ static int power_pmu_event_init(struct p
    cpuhw->bhrb_filter = ppmu->bhrb_filter_map(
    event->attr.branch_sample_type);

    - if(cpuhw->bhrb_filter == -1)
    + if (cpuhw->bhrb_filter == -1) {
    + put_cpu_var(cpu_hw_events);
    return -EOPNOTSUPP;
    + }
    }

    put_cpu_var(cpu_hw_events);
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