FAILED: patch "[PATCH] IB/hfi1: Insure use of smp_processor_id() is preempt disabled" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b6d57e24ce6cc3df8a8845e1b193e88a65d501b1 Mon Sep 17 00:00:00 2001
From: Mike Marciniszyn <[email protected]>
Date: Mon, 29 Nov 2021 14:19:58 -0500
Subject: [PATCH] IB/hfi1: Insure use of smp_processor_id() is preempt disabled

The following BUG has just surfaced with our 5.16 testing:

  BUG: using smp_processor_id() in preemptible [00000000] code: mpicheck/1581081
  caller is sdma_select_user_engine+0x72/0x210 [hfi1]
  CPU: 0 PID: 1581081 Comm: mpicheck Tainted: G S                5.16.0-rc1+ #1
  Hardware name: Intel Corporation S2600WT2R/S2600WT2R, BIOS SE5C610.86B.01.01.0016.033120161139 03/31/2016
  Call Trace:
   <TASK>
   dump_stack_lvl+0x33/0x42
   check_preemption_disabled+0xbf/0xe0
   sdma_select_user_engine+0x72/0x210 [hfi1]
   ? _raw_spin_unlock_irqrestore+0x1f/0x31
   ? hfi1_mmu_rb_insert+0x6b/0x200 [hfi1]
   hfi1_user_sdma_process_request+0xa02/0x1120 [hfi1]
   ? hfi1_write_iter+0xb8/0x200 [hfi1]
   hfi1_write_iter+0xb8/0x200 [hfi1]
   do_iter_readv_writev+0x163/0x1c0
   do_iter_write+0x80/0x1c0
   vfs_writev+0x88/0x1a0
   ? recalibrate_cpu_khz+0x10/0x10
   ? ktime_get+0x3e/0xa0
   ? __fget_files+0x66/0xa0
   do_writev+0x65/0x100
   do_syscall_64+0x3a/0x80

Fix this long standing bug by moving the smp_processor_id() to after the rcu_read_lock().

The rcu_read_lock() implicitly disables preemption.

index 2b6c24b7b586..f07d328689d3 100644
@@ -838,8 +838,8 @@ struct sdma_engine *sdma_select_user_engine(struct hfi1_devdata *dd,
 	if (current->nr_cpus_allowed != 1)
 		goto out;
 
-	cpu_id = smp_processor_id();
 	rcu_read_lock();
+	cpu_id = smp_processor_id();
 	rht_node = rhashtable_lookup(dd->sdma_rht, &cpu_id,
 				     sdma_rht_params);