tree 58ec1b0292bad883170e59f7af0b80c9b33cfe0b
parent 0d9c038feff6f834ad9e5d88b66715235ab23ff3
author Thomas Richter <tmricht@linux.ibm.com> 1552920627 +0100
committer Martin Schwidefsky <schwidefsky@de.ibm.com> 1553761722 +0100

s390/cpumf: Fix warning from check_processor_id

Function __hw_perf_event_init() used a CPU variable without
ensuring CPU preemption has been disabled. This caused the
following warning in the kernel log:

  [ 7.277085] BUG: using smp_processor_id() in preemptible
                 [00000000] code: cf-csdiag/1892
  [ 7.277111] caller is cf_diag_event_init+0x13a/0x338
  [ 7.277122] CPU: 10 PID: 1892 Comm: cf-csdiag Not tainted
                 5.0.0-20190318.rc0.git0.9e1a11e0f602.300.fc29.s390x+debug #1
  [ 7.277131] Hardware name: IBM 2964 NC9 712 (LPAR)
  [ 7.277139] Call Trace:
  [ 7.277150] ([<000000000011385a>] show_stack+0x82/0xd0)
  [ 7.277161]  [<0000000000b7a71a>] dump_stack+0x92/0xd0
  [ 7.277174]  [<00000000007b7e9c>] check_preemption_disabled+0xe4/0x100
  [ 7.277183]  [<00000000001228aa>] cf_diag_event_init+0x13a/0x338
  [ 7.277195]  [<00000000002cf3aa>] perf_try_init_event+0x72/0xf0
  [ 7.277204]  [<00000000002d0bba>] perf_event_alloc+0x6fa/0xce0
  [ 7.277214]  [<00000000002dc4a8>] __s390x_sys_perf_event_open+0x398/0xd50
  [ 7.277224]  [<0000000000b9e8f0>] system_call+0xdc/0x2d8
  [ 7.277233] 2 locks held by cf-csdiag/1892:
  [ 7.277241]  #0: 00000000976f5510 (&sig->cred_guard_mutex){+.+.},
                  at: __s390x_sys_perf_event_open+0xd2e/0xd50
  [ 7.277257]  #1: 00000000363b11bd (&pmus_srcu){....},
                  at: perf_event_alloc+0x52e/0xce0

The variable is now accessed in proper context. Use
get_cpu_var()/put_cpu_var() pair to disable
preemption during access.
As the hardware authorization settings apply to all CPUs, it
does not matter which CPU is used to check the authorization setting.

Remove the event->count assignment. It is not needed as function
perf_event_alloc() allocates memory for the event with kzalloc() and
thus count is already set to zero.

Fixes: fe5908bccc56 ("s390/cpum_cf_diag: Add support for s390 counter facility diagnostic trace")

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>