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From:   Uros Bizjak <ubizjak@gmail.com>
To:     linux-kernel@vger.kernel.org, x86@kernel.org,
        xen-devel@lists.xenproject.org
Cc:     Uros Bizjak <ubizjak@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Subject: [PATCH 3/3] xen: Illustrate the transition to sync_try_cmpxchg
Date:   Mon, 10 Jul 2023 21:21:56 +0200
Message-ID: <20230710192440.47140-3-ubizjak@gmail.com>
In-Reply-To: <20230710192440.47140-1-ubizjak@gmail.com>
References: <20230710192440.47140-1-ubizjak@gmail.com>
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This patch illustrates the transition to sync_try_cmpxchg.
It is not intended to be merged as-is.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
 drivers/xen/events/events_fifo.c | 26 ++++++++++++--------------
 drivers/xen/grant-table.c        | 10 ++++------
 2 files changed, 16 insertions(+), 20 deletions(-)

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index ad9fe51d3fb3..655775db7caf 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -226,21 +226,20 @@ static bool evtchn_fifo_is_masked(evtchn_port_t port)
  */
 static bool clear_masked_cond(volatile event_word_t *word)
 {
-	event_word_t new, old, w;
+	event_word_t new, old;
 
-	w = *word;
+	old = *word;
 
 	do {
-		if (!(w & (1 << EVTCHN_FIFO_MASKED)))
+		if (!(old & (1 << EVTCHN_FIFO_MASKED)))
 			return true;
 
-		if (w & (1 << EVTCHN_FIFO_PENDING))
+		if (old & (1 << EVTCHN_FIFO_PENDING))
 			return false;
 
-		old = w & ~(1 << EVTCHN_FIFO_BUSY);
+		old = old & ~(1 << EVTCHN_FIFO_BUSY);
 		new = old & ~(1 << EVTCHN_FIFO_MASKED);
-		w = sync_cmpxchg(word, old, new);
-	} while (w != old);
+	} while (!sync_try_cmpxchg(word, &old, new));
 
 	return true;
 }
@@ -259,17 +258,16 @@ static void evtchn_fifo_unmask(evtchn_port_t port)
 
 static uint32_t clear_linked(volatile event_word_t *word)
 {
-	event_word_t new, old, w;
+	event_word_t new, old;
 
-	w = *word;
+	old = *word;
 
 	do {
-		old = w;
-		new = (w & ~((1 << EVTCHN_FIFO_LINKED)
-			     | EVTCHN_FIFO_LINK_MASK));
-	} while ((w = sync_cmpxchg(word, old, new)) != old);
+		new = (old & ~((1 << EVTCHN_FIFO_LINKED)
+			       | EVTCHN_FIFO_LINK_MASK));
+	} while (!sync_try_cmpxchg(word, &old, new));
 
-	return w & EVTCHN_FIFO_LINK_MASK;
+	return old & EVTCHN_FIFO_LINK_MASK;
 }
 
 static void consume_one_event(unsigned cpu, struct evtchn_loop_ctrl *ctrl,
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index e1ec725c2819..211d083d4fbe 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -427,16 +427,14 @@ EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access);
 
 static int gnttab_end_foreign_access_ref_v1(grant_ref_t ref)
 {
-	u16 flags, nflags;
-	u16 *pflags;
+	u16 *pflags = &gnttab_shared.v1[ref].flags;
+	u16 flags;
 
-	pflags = &gnttab_shared.v1[ref].flags;
-	nflags = *pflags;
+	flags = *pflags;
 	do {
-		flags = nflags;
 		if (flags & (GTF_reading|GTF_writing))
 			return 0;
-	} while ((nflags = sync_cmpxchg(pflags, flags, 0)) != flags);
+	} while (!sync_try_cmpxchg(pflags, &flags, 0));
 
 	return 1;
 }
-- 
2.41.0