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Darwish" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1598528448; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=26R9zahhoyqsZTU4t3ThQWnrhdQZn+07MTILm+kfM9s=; b=TX1+1wjanjrE/bOMnAQJie2vzXwTv8I0mkZYGbi/xU31jqm7ZFLfRE5JIId1euJZdx1fBC 6D3SFXifQe3Ah1JhIdhmk7X43ZLaC5aYb8qe4sqHU/Uwg/IiMPlNn/1B4OoxerZuP8VlO5 EoFwQ9a7hRIF5bvQTQ9ciobIPaIS2QKmB3VTNcgzlxlKr/QZu/bY4ILbzmRXydf+vsAAeo tJWMORL7SJlZyv4VAHjp5Lx/jcd/DbBO/Z4jF5zAA6kp6A+sj2M60omDGkj4T7dILH/5Th rh/2ZCngAaSjLIMxKU0XoB1k0A99UCf46JEUMj5Pc+zqzvLgGAwPkvu+67ApdA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1598528448; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=26R9zahhoyqsZTU4t3ThQWnrhdQZn+07MTILm+kfM9s=; b=FXAOT/ODjYG0Jo2PimtDdINR90AKk8xVV8aVgquY793/G71eFay0QrpsWD+Oi8gUZDP9xw I9O81Vd9Q6hGHOAw== To: Peter Zijlstra , Ingo Molnar , Will Deacon Cc: Thomas Gleixner , "Sebastian A. Siewior" , LKML , "Ahmed S. Darwish" Subject: [PATCH v1 5/8] timekeeping: Use seqcount_latch_t Date: Thu, 27 Aug 2020 13:40:41 +0200 Message-Id: <20200827114044.11173-6-a.darwish@linutronix.de> In-Reply-To: <20200827114044.11173-1-a.darwish@linutronix.de> References: <20200519214547.352050-1-a.darwish@linutronix.de> <20200827114044.11173-1-a.darwish@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Latch sequence counters are a multiversion concurrency control mechanism where the seqcount_t counter even/odd value is used to switch between two data storage copies. This allows the seqcount_t read path to safely interrupt its write side critical section (e.g. from NMIs). Initially, latch sequence counters were implemented as a single write function, raw_write_seqcount_latch(), above plain seqcount_t. The read path was expected to use plain seqcount_t raw_read_seqcount(). A specialized read function was later added, raw_read_seqcount_latch(), and became the standardized way for latch read paths. Having unique read and write APIs meant that latch sequence counters are basically a data type of their own -- just inappropriately overloading plain seqcount_t. The seqcount_latch_t data type was thus introduced at seqlock.h. Use that new data type instead of seqcount_raw_spinlock_t. This ensures that only latch-safe APIs are to be used with the sequence counter. Note that the use of seqcount_raw_spinlock_t was not very useful in the first place. Only the "raw_" subset of seqcount_t APIs were used at timekeeping.c. This subset was created for contexts where lockdep cannot be used. seqcount_LOCKTYPE_t's raison d'être -- verifying that the seqcount_t writer serialization lock is held -- cannot thus be done. References: 0c3351d451ae ("seqlock: Use raw_ prefix instead of _no_lockdep") References: 55f3560df975 ("seqlock: Extend seqcount API with associated locks") Signed-off-by: Ahmed S. Darwish --- kernel/time/timekeeping.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 4c47f388a83f..999c981ae766 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -64,7 +64,7 @@ static struct timekeeper shadow_timekeeper; * See @update_fast_timekeeper() below. */ struct tk_fast { - seqcount_raw_spinlock_t seq; + seqcount_latch_t seq; struct tk_read_base base[2]; }; @@ -81,13 +81,13 @@ static struct clocksource dummy_clock = { }; static struct tk_fast tk_fast_mono ____cacheline_aligned = { - .seq = SEQCNT_RAW_SPINLOCK_ZERO(tk_fast_mono.seq, &timekeeper_lock), + .seq = SEQCNT_LATCH_ZERO(tk_fast_mono.seq), .base[0] = { .clock = &dummy_clock, }, .base[1] = { .clock = &dummy_clock, }, }; static struct tk_fast tk_fast_raw ____cacheline_aligned = { - .seq = SEQCNT_RAW_SPINLOCK_ZERO(tk_fast_raw.seq, &timekeeper_lock), + .seq = SEQCNT_LATCH_ZERO(tk_fast_raw.seq), .base[0] = { .clock = &dummy_clock, }, .base[1] = { .clock = &dummy_clock, }, }; @@ -467,7 +467,7 @@ static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf) tk_clock_read(tkr), tkr->cycle_last, tkr->mask)); - } while (read_seqcount_retry(&tkf->seq, seq)); + } while (read_seqcount_latch_retry(&tkf->seq, seq)); return now; } @@ -533,7 +533,7 @@ static __always_inline u64 __ktime_get_real_fast_ns(struct tk_fast *tkf) tk_clock_read(tkr), tkr->cycle_last, tkr->mask)); - } while (read_seqcount_retry(&tkf->seq, seq)); + } while (read_seqcount_latch_retry(&tkf->seq, seq)); return now; } -- 2.28.0