linux-kernel - [PATCH 23/34] RDMA/rtrs: fix opencoded find_and_set_bit_lock() in __rtrs_get

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Date:   Sat, 18 Nov 2023 07:50:54 -0800
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org,
        "Md. Haris Iqbal" <haris.iqbal@...os.com>,
        Jack Wang <jinpu.wang@...os.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>, linux-rdma@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>, Jan Kara <jack@...e.cz>,
        Mirsad Todorovac <mirsad.todorovac@....unizg.hr>,
        Matthew Wilcox <willy@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Alexey Klimov <klimov.linux@...il.com>
Subject: [PATCH 23/34] RDMA/rtrs: fix opencoded find_and_set_bit_lock() in __rtrs_get_permit()

The function opencodes find_and_set_bit_lock() with a while-loop polling
on test_and_set_bit_lock(). Use a dedicated find_and_set_bit_lock()
instead.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 drivers/infiniband/ulp/rtrs/rtrs-clt.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/drivers/infiniband/ulp/rtrs/rtrs-clt.c b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
index 07261523c554..2f3b0ad42e8a 100644
--- a/drivers/infiniband/ulp/rtrs/rtrs-clt.c
+++ b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
@@ -72,18 +72,9 @@ __rtrs_get_permit(struct rtrs_clt_sess *clt, enum rtrs_clt_con_type con_type)
 	struct rtrs_permit *permit;
 	int bit;
 
-	/*
-	 * Adapted from null_blk get_tag(). Callers from different cpus may
-	 * grab the same bit, since find_first_zero_bit is not atomic.
-	 * But then the test_and_set_bit_lock will fail for all the
-	 * callers but one, so that they will loop again.
-	 * This way an explicit spinlock is not required.
-	 */
-	do {
-		bit = find_first_zero_bit(clt->permits_map, max_depth);
-		if (bit >= max_depth)
-			return NULL;
-	} while (test_and_set_bit_lock(bit, clt->permits_map));
+	bit = find_and_set_bit_lock(clt->permits_map, max_depth);
+	if (bit >= max_depth)
+		return NULL;
 
 	permit = get_permit(clt, bit);
 	WARN_ON(permit->mem_id != bit);
-- 
2.39.2