From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtpweb147.aruba.it (smtpweb147.aruba.it [62.149.158.147]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CA37A37B41A for ; Fri, 10 Apr 2026 12:23:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.149.158.147 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775823807; cv=none; b=o9/ZAvFlaS0gxz9kY01LhUVrRbAvwlR3ESypuNSHeat5KmDGLx26Nj54GWXX5wwEud2JcVVOD47drDGIKYg2F3DeWJP3Fy2tnOfCadcN00ey0ApD9ScwAPK4AEHfEv7MA27vJ/Iwlp4Pt5IAmyn2cbMeOcaNQ1Nt+bn540N6QRc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775823807; c=relaxed/simple; bh=IUNKrU08ZPhvJyPOzJRjQI9TrAGrouVqJm1M/WIYzmU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aakyA/425yJrq0A4hx65rt7IC1g81mqVMa+MaoUlNdmy3FUQMEmAsI1F6gN+3wE+FMvGgRcvnIPC0jpQYErypJjRv4BnCyNWtugMayE7CwCbm2wMlRXkfe+bQK/5YfuJ3QrC0tfsLDVT1VpNlyvsjpa2EhuDjvGxX9aNb9MjFI0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=enneenne.com; spf=pass smtp.mailfrom=enneenne.com; dkim=pass (2048-bit key) header.d=aruba.it header.i=@aruba.it header.b=nW20SnqN; arc=none smtp.client-ip=62.149.158.147 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=enneenne.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=enneenne.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=aruba.it header.i=@aruba.it header.b="nW20SnqN" Received: from [192.168.1.58] ([79.0.204.227]) by Aruba SMTP with ESMTPSA id BAqMwLenVrbJKBAqMwWNpF; Fri, 10 Apr 2026 14:20:14 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=aruba.it; s=a1; t=1775823614; bh=IUNKrU08ZPhvJyPOzJRjQI9TrAGrouVqJm1M/WIYzmU=; h=Date:MIME-Version:Subject:To:From:Content-Type; b=nW20SnqNd7Um4FBBZ+Mqv7Q83k7Y+Di6wU5slA1pY7TteqO8Ya/ajg9aKlhY5zyco mI9B2WrjLuANh0n9Y6DEo1QB74W7jgUj3h50Cf/EVIOqockp+BpAQAa/0Om04e5BTJ L0s6DbQMzgyd2gBHXRqLR3rTeisdu4iI/YvZGH8GRdoN6YJi/n9uQmSNT7SBHvw7dg Hc5K3Q61nCJuKpyhAsY9QOGf68BuMGSlu0kAaEszuEKGdfmUN739O4zQJ6buATz4eq 5MAxmMMTob1Q/rxLufkrMs2z9OZ9Lzs+Lyfrqt8CtbqU2huciI+EjB1y3jvKb8RpEG 89HnCRWXB/Asw== Message-ID: Date: Fri, 10 Apr 2026 14:20:14 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/3] pps: convert pps_device lock to raw_spinlock for PREEMPT_RT Content-Language: en-US To: Michael Byczkowski Cc: Andrew Morton , linux-kernel@vger.kernel.org References: <4D388402-C22B-4BF2-B739-67ED7FC30999@by-online.de> <4E1D2A95-EA2C-436A-9E1A-8AD67C043D56@by-online.de> <4415F5E2-E9DB-4CFC-BF23-6906245041DF@by-online.de> From: Rodolfo Giometti In-Reply-To: <4415F5E2-E9DB-4CFC-BF23-6906245041DF@by-online.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CMAE-Envelope: MS4xfKkYKWMtltL6jyrysI6FdTHPsUIanWlHyLabvzVUkhJ05oAS+VZ5GyZLV28hl10sXdhsyAXPn4ZwK4okU9dfTJYGNHnzsB9gzs82tJ8TWNH9Z+O96jkF 2bYC/bRmXx83fBH/MVpwQ5S9B7C7hp2XlEF4mmP2vSirnWgGXrofrTRRauVTli639VqP38pG2OO1s8vN70lTEyyCbAZOhVKlq7p1yNrAMDMXiNjAShreuVN+ WDE7DCVPzvI805tLdGD0Uak2kEzU2QP2EUqydW4Xlxs= On 4/10/26 12:17, Michael Byczkowski wrote: > On PREEMPT_RT, spinlock_t becomes a sleeping mutex, which allows > pps_event() to be preempted mid-update by other RT threads. This > introduces jitter in the PPS event recording path. > > Convert pps_device.lock to raw_spinlock_t so the timestamp and > sequence number updates remain non-preemptible on RT. > > Move wake_up_interruptible_all() and kill_fasync() outside the > raw_spinlock critical section, as these acquire sleeping locks > on PREEMPT_RT. The lock now protects only the timestamp, sequence > number, and last_ev updates. This is safe because PPS_FETCH waiters > use wait_event_interruptible_timeout() and will re-check after > waking, and kill_fasync() does not require PPS data to be locked > (thanks to Nikolaus Buchwitz for reporting). > > On non-RT kernels, raw_spinlock_t compiles to identical code as > spinlock_t — no behavioral change. > > Signed-off-by: Michael Byczkowski Acked-by: Rodolfo Giometti > Tested-by: Michael Byczkowski > --- > drivers/pps/kapi.c | 18 +++++++++++------- > drivers/pps/pps.c | 16 ++++++++-------- > include/linux/pps_kernel.h | 2 +- > 3 files changed, 20 insertions(+), 16 deletions(-) > > diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c > index 1bf0335a1b41..46d9fe8b8ce9 100644 > --- a/drivers/pps/kapi.c > +++ b/drivers/pps/kapi.c > @@ -102,7 +102,7 @@ struct pps_device *pps_register_source(struct pps_source_info *info, > pps->info.echo = pps_echo_client_default; > > init_waitqueue_head(&pps->queue); > - spin_lock_init(&pps->lock); > + raw_spin_lock_init(&pps->lock); > > /* Create the char device */ > err = pps_register_cdev(pps); > @@ -167,7 +167,7 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event, > > timespec_to_pps_ktime(&ts_real, ts->ts_real); > > - spin_lock_irqsave(&pps->lock, flags); > + raw_spin_lock_irqsave(&pps->lock, flags); > > /* Must call the echo function? */ > if ((pps->params.mode & (PPS_ECHOASSERT | PPS_ECHOCLEAR))) > @@ -206,14 +206,18 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event, > > pps_kc_event(pps, ts, event); > > - /* Wake up if captured something */ > - if (captured) { > + if (captured) > pps->last_ev++; > - wake_up_interruptible_all(&pps->queue); > > + raw_spin_unlock_irqrestore(&pps->lock, flags); > + > + /* > + * Wake up after releasing the lock: wake_up_interruptible_all() > + * and kill_fasync() acquire sleeping locks on PREEMPT_RT. > + */ > + if (captured) { > + wake_up_interruptible_all(&pps->queue); > kill_fasync(&pps->async_queue, SIGIO, POLL_IN); > } > - > - spin_unlock_irqrestore(&pps->lock, flags); > } > EXPORT_SYMBOL(pps_event); > diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c > index c6b8b6478276..ad96425208a1 100644 > --- a/drivers/pps/pps.c > +++ b/drivers/pps/pps.c > @@ -103,12 +103,12 @@ static long pps_cdev_ioctl(struct file *file, > case PPS_GETPARAMS: > dev_dbg(&pps->dev, "PPS_GETPARAMS\n"); > > - spin_lock_irq(&pps->lock); > + raw_spin_lock_irq(&pps->lock); > > /* Get the current parameters */ > params = pps->params; > > - spin_unlock_irq(&pps->lock); > + raw_spin_unlock_irq(&pps->lock); > > err = copy_to_user(uarg, ¶ms, sizeof(struct pps_kparams)); > if (err) > @@ -139,7 +139,7 @@ static long pps_cdev_ioctl(struct file *file, > return -EINVAL; > } > > - spin_lock_irq(&pps->lock); > + raw_spin_lock_irq(&pps->lock); > > /* Save the new parameters */ > pps->params = params; > @@ -163,7 +163,7 @@ static long pps_cdev_ioctl(struct file *file, > pps->params.assert_off_tu.flags = 0; > pps->params.clear_off_tu.flags = 0; > > - spin_unlock_irq(&pps->lock); > + raw_spin_unlock_irq(&pps->lock); > > break; > > @@ -190,7 +190,7 @@ static long pps_cdev_ioctl(struct file *file, > return err; > > /* Return the fetched timestamp and save last fetched event */ > - spin_lock_irq(&pps->lock); > + raw_spin_lock_irq(&pps->lock); > > pps->last_fetched_ev = pps->last_ev; > > @@ -200,7 +200,7 @@ static long pps_cdev_ioctl(struct file *file, > fdata.info.clear_tu = pps->clear_tu; > fdata.info.current_mode = pps->current_mode; > > - spin_unlock_irq(&pps->lock); > + raw_spin_unlock_irq(&pps->lock); > > err = copy_to_user(uarg, &fdata, sizeof(struct pps_fdata)); > if (err) > @@ -278,7 +278,7 @@ static long pps_cdev_compat_ioctl(struct file *file, > return err; > > /* Return the fetched timestamp and save last fetched event */ > - spin_lock_irq(&pps->lock); > + raw_spin_lock_irq(&pps->lock); > > pps->last_fetched_ev = pps->last_ev; > > @@ -291,7 +291,7 @@ static long pps_cdev_compat_ioctl(struct file *file, > memcpy(&compat.info.clear_tu, &pps->clear_tu, > sizeof(struct pps_ktime_compat)); > > - spin_unlock_irq(&pps->lock); > + raw_spin_unlock_irq(&pps->lock); > > return copy_to_user(uarg, &compat, > sizeof(struct pps_fdata_compat)) ? -EFAULT : 0; > diff --git a/include/linux/pps_kernel.h b/include/linux/pps_kernel.h > index aab0aebb529e..f2fe504071ed 100644 > --- a/include/linux/pps_kernel.h > +++ b/include/linux/pps_kernel.h > @@ -59,7 +59,7 @@ struct pps_device { > void const *lookup_cookie; /* For pps_lookup_dev() only */ > struct device dev; > struct fasync_struct *async_queue; /* fasync method */ > - spinlock_t lock; > + raw_spinlock_t lock; > }; > > /* -- GNU/Linux Solutions e-mail: giometti@enneenne.com Linux Device Driver giometti@linux.it Embedded Systems phone: +39 349 2432127 UNIX programming