1. 04 Dec, 2018 2 commits
    • Breno Leitao's avatar
      powerpc/pseries/cpuidle: Fix preempt warning · 2b038cbc
      Breno Leitao authored
      When booting a pseries kernel with PREEMPT enabled, it dumps the
      following warning:
      
         BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
         caller is pseries_processor_idle_init+0x5c/0x22c
         CPU: 13 PID: 1 Comm: swapper/0 Not tainted 4.20.0-rc3-00090-g12201a0128bc-dirty #828
         Call Trace:
         [c000000429437ab0] [c0000000009c8878] dump_stack+0xec/0x164 (unreliable)
         [c000000429437b00] [c0000000005f2f24] check_preemption_disabled+0x154/0x160
         [c000000429437b90] [c000000000cab8e8] pseries_processor_idle_init+0x5c/0x22c
         [c000000429437c10] [c000000000010ed4] do_one_initcall+0x64/0x300
         [c000000429437ce0] [c000000000c54500] kernel_init_freeable+0x3f0/0x500
         [c000000429437db0] [c0000000000112dc] kernel_init+0x2c/0x160
         [c000000429437e20] [c00000000000c1d0] ret_from_kernel_thread+0x5c/0x6c
      
      This happens because the code calls get_lppaca() which calls
      get_paca() and it checks if preemption is disabled through
      check_preemption_disabled().
      
      Preemption should be disabled because the per CPU variable may make no
      sense if there is a preemption (and a CPU switch) after it reads the
      per CPU data and when it is used.
      
      In this device driver specifically, it is not a problem, because this
      code just needs to have access to one lppaca struct, and it does not
      matter if it is the current per CPU lppaca struct or not (i.e. when
      there is a preemption and a CPU migration).
      
      That said, the most appropriate fix seems to be related to avoiding
      the debug_smp_processor_id() call at get_paca(), instead of calling
      preempt_disable() before get_paca().
      Signed-off-by: default avatarBreno Leitao <leitao@debian.org>
      Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
      2b038cbc
    • Breno Leitao's avatar
      powerpc/xmon: Fix invocation inside lock region · 8d4a8622
      Breno Leitao authored
      Currently xmon needs to get devtree_lock (through rtas_token()) during its
      invocation (at crash time). If there is a crash while devtree_lock is being
      held, then xmon tries to get the lock but spins forever and never get into
      the interactive debugger, as in the following case:
      
      	int *ptr = NULL;
      	raw_spin_lock_irqsave(&devtree_lock, flags);
      	*ptr = 0xdeadbeef;
      
      This patch avoids calling rtas_token(), thus trying to get the same lock,
      at crash time. This new mechanism proposes getting the token at
      initialization time (xmon_init()) and just consuming it at crash time.
      
      This would allow xmon to be possible invoked independent of devtree_lock
      being held or not.
      Signed-off-by: default avatarBreno Leitao <leitao@debian.org>
      Reviewed-by: default avatarThiago Jung Bauermann <bauerman@linux.ibm.com>
      Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
      8d4a8622
  2. 26 Nov, 2018 17 commits
  3. 25 Nov, 2018 21 commits