From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752850AbbCZTXl (ORCPT ); Thu, 26 Mar 2015 15:23:41 -0400 Received: from mail-pa0-f50.google.com ([209.85.220.50]:33097 "EHLO mail-pa0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751997AbbCZTXe (ORCPT ); Thu, 26 Mar 2015 15:23:34 -0400 From: John Stultz To: lkml Cc: Daniel Thompson , Russell King , Will Deacon , Catalin Marinas , Thomas Gleixner , Stephen Boyd , Peter Zijlstra , Ingo Molnar , John Stultz Subject: [PATCH 1/5] sched_clock: Match scope of read and write seqcounts Date: Thu, 26 Mar 2015 12:23:22 -0700 Message-Id: <1427397806-20889-2-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1427397806-20889-1-git-send-email-john.stultz@linaro.org> References: <1427397806-20889-1-git-send-email-john.stultz@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Daniel Thompson Currently the scope of the raw_write_seqcount_begin/end in sched_clock_register far exceeds the scope of the read section in sched_clock. This gives the impression of safety during cursory review but achieves little. Note that this is likely to be a latent issue at present because sched_clock_register() is typically called before we enable interrupts, however the issue does risk bugs being needlessly introduced as the code evolves. This patch fixes the problem by increasing the scope of the read locking performed by sched_clock() to cover all data modified by sched_clock_register. We also improve clarity by moving writes to struct clock_data that do not impact sched_clock() outside of the critical section. Cc: Russell King Cc: Will Deacon Cc: Catalin Marinas Cc: Daniel Thompson Cc: Thomas Gleixner Cc: Stephen Boyd Cc: Peter Zijlstra Cc: Ingo Molnar Reviewed-by: Stephen Boyd Acked-by: Peter Zijlstra (Intel) Signed-off-by: Daniel Thompson [jstultz: Slight rework to apply to tip/timers/core] Signed-off-by: John Stultz --- kernel/time/sched_clock.c | 26 +++++++++++--------------- 1 file changed, 11 insertions(+), 15 deletions(-) diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c index ca3bc5c..1751e95 100644 --- a/kernel/time/sched_clock.c +++ b/kernel/time/sched_clock.c @@ -58,23 +58,21 @@ static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift) unsigned long long notrace sched_clock(void) { - u64 epoch_ns; - u64 epoch_cyc; - u64 cyc; + u64 cyc, res; unsigned long seq; - if (cd.suspended) - return cd.epoch_ns; - do { seq = raw_read_seqcount_begin(&cd.seq); - epoch_cyc = cd.epoch_cyc; - epoch_ns = cd.epoch_ns; + + res = cd.epoch_ns; + if (!cd.suspended) { + cyc = read_sched_clock(); + cyc = (cyc - cd.epoch_cyc) & sched_clock_mask; + res += cyc_to_ns(cyc, cd.mult, cd.shift); + } } while (read_seqcount_retry(&cd.seq, seq)); - cyc = read_sched_clock(); - cyc = (cyc - epoch_cyc) & sched_clock_mask; - return epoch_ns + cyc_to_ns(cyc, cd.mult, cd.shift); + return res; } /* @@ -111,7 +109,6 @@ void __init sched_clock_register(u64 (*read)(void), int bits, { u64 res, wrap, new_mask, new_epoch, cyc, ns; u32 new_mult, new_shift; - ktime_t new_wrap_kt; unsigned long r; char r_unit; @@ -124,10 +121,11 @@ void __init sched_clock_register(u64 (*read)(void), int bits, clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600); new_mask = CLOCKSOURCE_MASK(bits); + cd.rate = rate; /* calculate how many nanosecs until we risk wrapping */ wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL); - new_wrap_kt = ns_to_ktime(wrap); + cd.wrap_kt = ns_to_ktime(wrap); /* update epoch for new counter and update epoch_ns from old counter*/ new_epoch = read(); @@ -138,8 +136,6 @@ void __init sched_clock_register(u64 (*read)(void), int bits, raw_write_seqcount_begin(&cd.seq); read_sched_clock = read; sched_clock_mask = new_mask; - cd.rate = rate; - cd.wrap_kt = new_wrap_kt; cd.mult = new_mult; cd.shift = new_shift; cd.epoch_cyc = new_epoch; -- 1.9.1