From: Davidlohr Bueso Date: Fri, 6 May 2022 10:57:57 +0000 (+0200) Subject: scsi: libfc: Remove get_cpu() semantics in fc_exch_em_alloc() X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=a0548edf852a8776dade1e511694b2980c674e2a;p=linux.git scsi: libfc: Remove get_cpu() semantics in fc_exch_em_alloc() The get_cpu() in fc_exch_em_alloc() was introduced in commit f018b73af6db ("[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 --- 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) {