From c25e2cb8289927b0668197477cfc641a73ab79d1 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Fri, 6 May 2022 12:57:57 +0200 Subject: [PATCH] scsi: libfc: Remove get_cpu() semantics in fc_exch_em_alloc() The get_cpu() in fc_exch_em_alloc() was introduced in commit 9c58f277f90b ("[SCSI] libfc, libfcoe, fcoe: use smp_processor_id() only when preempt disabled") for no other reason than to simply use smp_processor_id() without getting a warning, because everything is done with the pool->lock held anyway. However, get_cpu(), by disabling preemption, does not play well with PREEMPT_RT, particularly when acquiring a regular (and thus sleepable) spinlock. Therefore remove the get_cpu() and just use the unstable value as we will have CPU locality guarantees next by taking the lock. The window of migration, as noted by Sebastian, is small and even if it happens the result is correct. Link: https://lore.kernel.org/r/20211117025956.79616-2-dave@stgolabs.net Link: https://lore.kernel.org/r/20220506105758.283887-4-bigeasy@linutronix.de Acked-by: Sebastian Andrzej Siewior Signed-off-by: Davidlohr Bueso Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Martin K. Petersen --- drivers/scsi/libfc/fc_exch.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/drivers/scsi/libfc/fc_exch.c b/drivers/scsi/libfc/fc_exch.c index aa223db4cf53c..1d91c457527f3 100644 --- a/drivers/scsi/libfc/fc_exch.c +++ b/drivers/scsi/libfc/fc_exch.c @@ -825,10 +825,9 @@ static struct fc_exch *fc_exch_em_alloc(struct fc_lport *lport, } memset(ep, 0, sizeof(*ep)); - cpu = get_cpu(); + cpu = raw_smp_processor_id(); pool = per_cpu_ptr(mp->pool, cpu); spin_lock_bh(&pool->lock); - put_cpu(); /* peek cache of free slot */ if (pool->left != FC_XID_UNKNOWN) { -- 2.39.5