RE: [PATCH] soc: fsl: dpio: protect smp_processor_id when get processor id

-----Original Message-----
From: Robin Murphy <robin.murphy@arm.com>
Sent: Friday, October 15, 2021 9:40 PM
To: Li, Meng <redacted>; Roy.Pledge@nxp.com;
leoyang.li@nxp.com; ruxandra.radulescu@nxp.com; horia.geanta@nxp.com
Cc: linux-kernel@vger.kernel.org; linuxppc-dev@lists.ozlabs.org; linux-arm-
kernel@lists.infradead.org
Subject: Re: [PATCH] soc: fsl: dpio: protect smp_processor_id when get
processor id

[Please note: This e-mail is from an EXTERNAL e-mail address]

On 2021-10-15 07:36, Meng.Li@windriver.com wrote:

quoted

From: Meng Li <redacted>

When enable debug kernel configs,there will be calltrace as below:

BUG: using smp_processor_id() in preemptible [00000000] code:
swapper/0/1 caller is debug_smp_processor_id+0x20/0x30
CPU: 6 PID: 1 Comm: swapper/0 Not tainted 5.10.63-yocto-standard #1
Hardware name: NXP Layerscape LX2160ARDB (DT) Call trace:
  dump_backtrace+0x0/0x1a0
  show_stack+0x24/0x30
  dump_stack+0xf0/0x13c
  check_preemption_disabled+0x100/0x110
  debug_smp_processor_id+0x20/0x30
  dpaa2_io_query_fq_count+0xdc/0x154
  dpaa2_eth_stop+0x144/0x314
  __dev_close_many+0xdc/0x160
  __dev_change_flags+0xe8/0x220
  dev_change_flags+0x30/0x70
  ic_close_devs+0x50/0x78
  ip_auto_config+0xed0/0xf10
  do_one_initcall+0xac/0x460
  kernel_init_freeable+0x30c/0x378
  kernel_init+0x20/0x128
  ret_from_fork+0x10/0x38

Because smp_processor_id() should be invoked in preempt disable status.
So, add preempt_disable/enable() to protect smp_processor_id().

If preemption doesn't matter anyway, as the comment in the context implies,
then it probably makes more sense just to use
raw_smp_processor_id() instead.

Thanks for your professional suggest, I will raw_smp_processor_id() and test.
If works fine, I will send v2 patch.

Thanks,
Limeng

Robin.

quoted

Fixes: c89105c9b390 ("staging: fsl-mc: Move DPIO from staging to
drivers/soc/fsl")
Cc: stable@vger.kernel.org
Signed-off-by: Meng Li <redacted>
---
  drivers/soc/fsl/dpio/dpio-service.c | 7 +++++--
  1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/soc/fsl/dpio/dpio-service.c

b/drivers/soc/fsl/dpio/dpio-service.c
index 19f47ea9dab0..afc3b89b0fc5 100644

--- a/drivers/soc/fsl/dpio/dpio-service.c
+++ b/drivers/soc/fsl/dpio/dpio-service.c

@@ -58,8 +58,11 @@ static inline struct dpaa2_io

*service_select_by_cpu(struct dpaa2_io *d,

quoted

       * If cpu == -1, choose the current cpu, with no guarantees about
       * potentially being migrated away.
       */
-     if (cpu < 0)
-             cpu = smp_processor_id();
+        if (cpu < 0) {
+                preempt_disable();
+                cpu = smp_processor_id();
+                preempt_enable();
+        }

      /* If a specific cpu was requested, pick it up immediately */
      return dpio_by_cpu[cpu];

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