From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, torvalds@linux-foundation.org, mark.rutland@arm.com, dhowells@redhat.com, linux-arch@vger.kernel.org, peterz@infradead.org, will.deacon@arm.com, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, <linux-am33-list@redhat.com> Subject: [PATCH RFC tip/core/rcu 02/15] mn10300: READ_ONCE() now implies smp_read_barrier_depends() Date: Mon, 9 Oct 2017 17:22:36 -0700 [thread overview] Message-ID: <1507594969-8347-2-git-send-email-paulmck@linux.vnet.ibm.com> (raw) In-Reply-To: <20171010001951.GA6476@linux.vnet.ibm.com> Given that READ_ONCE() now implies smp_read_barrier_depends(), there is no need for the open-coded smp_read_barrier_depends() in mn10300_serial_receive_interrupt() and mn10300_serial_poll_get_char(). This commit therefore removes them, but replaces them with comments calling out that carrying dependencies through non-pointers is quite dangerous. Compilers simply know too much about integers. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: David Howells <dhowells@redhat.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: <linux-am33-list@redhat.com> --- arch/mn10300/kernel/mn10300-serial.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/mn10300/kernel/mn10300-serial.c b/arch/mn10300/kernel/mn10300-serial.c index d7ef1232a82a..4994b570dfd9 100644 --- a/arch/mn10300/kernel/mn10300-serial.c +++ b/arch/mn10300/kernel/mn10300-serial.c @@ -550,7 +550,7 @@ static void mn10300_serial_receive_interrupt(struct mn10300_serial_port *port) return; } - smp_read_barrier_depends(); + /* READ_ONCE() enforces dependency, but dangerous through integer!!! */ ch = port->rx_buffer[ix++]; st = port->rx_buffer[ix++]; smp_mb(); @@ -1728,7 +1728,10 @@ static int mn10300_serial_poll_get_char(struct uart_port *_port) if (CIRC_CNT(port->rx_inp, ix, MNSC_BUFFER_SIZE) == 0) return NO_POLL_CHAR; - smp_read_barrier_depends(); + /* + * READ_ONCE() enforces dependency, but dangerous + * through integer!!! + */ ch = port->rx_buffer[ix++]; st = port->rx_buffer[ix++]; smp_mb(); -- 2.5.2
WARNING: multiple messages have this Message-ID (diff)
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, torvalds@linux-foundation.org, mark.rutland@arm.com, dhowells@redhat.com, linux-arch@vger.kernel.org, peterz@infradead.org, will.deacon@arm.com, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, linux-am33-list@redhat.com Subject: [PATCH RFC tip/core/rcu 02/15] mn10300: READ_ONCE() now implies smp_read_barrier_depends() Date: Mon, 9 Oct 2017 17:22:36 -0700 [thread overview] Message-ID: <1507594969-8347-2-git-send-email-paulmck@linux.vnet.ibm.com> (raw) In-Reply-To: <20171010001951.GA6476@linux.vnet.ibm.com> Given that READ_ONCE() now implies smp_read_barrier_depends(), there is no need for the open-coded smp_read_barrier_depends() in mn10300_serial_receive_interrupt() and mn10300_serial_poll_get_char(). This commit therefore removes them, but replaces them with comments calling out that carrying dependencies through non-pointers is quite dangerous. Compilers simply know too much about integers. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: David Howells <dhowells@redhat.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: <linux-am33-list@redhat.com> --- arch/mn10300/kernel/mn10300-serial.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/mn10300/kernel/mn10300-serial.c b/arch/mn10300/kernel/mn10300-serial.c index d7ef1232a82a..4994b570dfd9 100644 --- a/arch/mn10300/kernel/mn10300-serial.c +++ b/arch/mn10300/kernel/mn10300-serial.c @@ -550,7 +550,7 @@ static void mn10300_serial_receive_interrupt(struct mn10300_serial_port *port) return; } - smp_read_barrier_depends(); + /* READ_ONCE() enforces dependency, but dangerous through integer!!! */ ch = port->rx_buffer[ix++]; st = port->rx_buffer[ix++]; smp_mb(); @@ -1728,7 +1728,10 @@ static int mn10300_serial_poll_get_char(struct uart_port *_port) if (CIRC_CNT(port->rx_inp, ix, MNSC_BUFFER_SIZE) == 0) return NO_POLL_CHAR; - smp_read_barrier_depends(); + /* + * READ_ONCE() enforces dependency, but dangerous + * through integer!!! + */ ch = port->rx_buffer[ix++]; st = port->rx_buffer[ix++]; smp_mb(); -- 2.5.2
next prev parent reply other threads:[~2017-10-10 0:23 UTC|newest] Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-10-10 0:19 [PATCH RFC tip/core/rcu 0/15] Remove to-be-unneeded smp_read_barrier_depends() Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 01/15] doc: READ_ONCE() now implies smp_barrier_depends() Paul E. McKenney 2017-10-10 0:22 ` Paul E. McKenney [this message] 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 02/15] mn10300: READ_ONCE() now implies smp_read_barrier_depends() Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 03/15] drivers/net/ethernet/qlogic/qed: Fix __qed_spq_block() ordering Paul E. McKenney 2017-10-10 0:22 ` Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 04/15] fs/dcache: Use release-acquire for name/length update Paul E. McKenney 2017-10-10 0:22 ` Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 05/15] percpu: READ_ONCE() now implies smp_read_barrier_depends() Paul E. McKenney 2017-10-10 14:08 ` Tejun Heo 2017-10-10 15:30 ` Paul E. McKenney 2017-10-10 15:49 ` Tejun Heo 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 06/15] rcu: Adjust read-side accessor comments for READ_ONCE() Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 07/15] rtnetlink: Update now-misleading smp_read_barrier_depends() comment Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 08/15] seqlock: Remove now-redundant smp_read_barrier_depends() Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 09/15] uprobes: " Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 10/15] locking: Remove smp_read_barrier_depends() from queued_spin_lock_slowpath() Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 11/15] tracepoint: Remove smp_read_barrier_depends() from comment Paul E. McKenney 2017-10-10 0:31 ` Steven Rostedt 2017-10-10 1:12 ` Mathieu Desnoyers 2017-10-10 15:32 ` Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier_depends() Paul E. McKenney 2017-10-10 8:39 ` Peter Zijlstra 2017-10-10 9:36 ` David Howells 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 13/15] mm/ksm: Remove now-redundant smp_read_barrier_depends() Paul E. McKenney 2017-10-10 0:22 ` Paul E. McKenney 2017-10-10 0:22 ` Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 14/15] netfilter: " Paul E. McKenney 2017-10-10 0:22 ` Paul E. McKenney 2017-10-10 8:43 ` Peter Zijlstra 2017-10-10 15:56 ` Paul E. McKenney 2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 15/15] keyring: " Paul E. McKenney 2017-10-10 0:22 ` Paul E. McKenney 2017-10-10 0:22 ` Paul E. McKenney 2017-10-10 0:22 ` Paul E. McKenney 2017-10-10 9:35 ` [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier_depends() David Howells 2017-10-10 15:50 ` Paul E. McKenney 2017-10-10 15:54 ` Peter Zijlstra 2017-10-10 16:05 ` Paul E. McKenney 2017-10-11 12:19 ` David Howells 2017-10-11 12:22 ` Will Deacon 2017-10-11 12:54 ` Paul E. McKenney 2017-10-11 14:18 ` Will Deacon 2017-10-11 14:50 ` Paul E. McKenney 2017-10-11 12:58 ` Paul E. McKenney 2017-10-11 15:17 ` David Howells 2017-10-11 15:59 ` Paul E. McKenney 2017-10-11 16:12 ` Peter Zijlstra 2017-10-11 16:24 ` Peter Zijlstra 2017-10-11 16:47 ` Paul E. McKenney 2017-10-11 16:54 ` Peter Zijlstra 2017-10-11 17:06 ` Paul E. McKenney 2017-10-11 17:11 ` Peter Zijlstra 2017-10-11 17:34 ` Paul E. McKenney 2017-10-11 18:43 ` Dmitry Vyukov 2017-10-11 18:56 ` Linus Torvalds 2017-10-11 19:28 ` Paul E. McKenney 2017-10-11 19:59 ` Dmitry Vyukov 2017-10-11 17:14 ` Paul E. McKenney 2017-10-11 17:19 ` Mark Rutland 2017-10-11 16:50 ` Paul E. McKenney 2017-10-11 16:07 ` David Howells 2017-10-11 16:17 ` Peter Zijlstra 2017-10-11 16:19 ` Paul E. McKenney 2017-10-11 15:28 ` David Howells 2017-10-11 16:02 ` Paul E. McKenney 2017-10-10 9:59 ` David Howells 2017-10-10 15:52 ` Paul E. McKenney 2017-10-11 12:21 ` [PATCH RFC tip/core/rcu 0/15] Remove to-be-unneeded smp_read_barrier_depends() David Howells 2017-10-11 12:56 ` Paul E. McKenney
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