From: Will Deacon <will.deacon@arm.com>
To: Julien Grall <julien.grall@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, tglx@linutronix.de,
rostedt@goodmis.org, bigeasy@linutronix.de,
suzuki.poulose@arm.com, catalin.marinas@arm.com,
dave.martin@arm.com
Subject: Re: [PATCH] arm64/cpufeature: Convert hook_lock to raw_spin_lock_t in cpu_enable_ssbs()
Date: Thu, 30 May 2019 13:01:29 +0100 [thread overview]
Message-ID: <20190530120129.GD13751@fuggles.cambridge.arm.com> (raw)
In-Reply-To: <20190530113058.1988-1-julien.grall@arm.com>
On Thu, May 30, 2019 at 12:30:58PM +0100, Julien Grall wrote:
> cpu_enable_ssbs() is called via stop_machine() as part of the cpu_enable
> callback. A spin lock is used to ensure the hook is registered before
> the rest of the callback is executed.
>
> On -RT spin_lock() may sleep. However, all the callees in stop_machine()
> are expected to not sleep. Therefore a raw_spin_lock() is required here.
>
> Given this is already done under stop_machine() and the work done under
> the lock is quite small, the latency should not increase too much.
>
> Signed-off-by: Julien Grall <julien.grall@arm.com>
>
> ---
>
> It was noticed when looking at the current use of spin_lock in
> arch/arm64. I don't have a platform calling that callback, so I have
> hacked the code to reproduce the error and check it is now fixed.
> ---
> arch/arm64/kernel/cpufeature.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index ca27e08e3d8a..2a7159fda3ce 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1194,14 +1194,14 @@ static struct undef_hook ssbs_emulation_hook = {
> static void cpu_enable_ssbs(const struct arm64_cpu_capabilities *__unused)
> {
> static bool undef_hook_registered = false;
> - static DEFINE_SPINLOCK(hook_lock);
> + static DEFINE_RAW_SPINLOCK(hook_lock);
>
> - spin_lock(&hook_lock);
> + raw_spin_lock(&hook_lock);
> if (!undef_hook_registered) {
> register_undef_hook(&ssbs_emulation_hook);
> undef_hook_registered = true;
> }
> - spin_unlock(&hook_lock);
> + raw_spin_unlock(&hook_lock);
Makes sense to me. We could probably avoid the lock entirely if we wanted
to (via atomic_dec_if_positive), but I'm not sure it's really worth it.
Will
next prev parent reply other threads:[~2019-05-30 12:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-30 11:30 [PATCH] arm64/cpufeature: Convert hook_lock to raw_spin_lock_t in cpu_enable_ssbs() Julien Grall
2019-05-30 12:01 ` Will Deacon [this message]
2019-05-30 13:55 ` Julien Grall
2019-06-04 13:49 ` Catalin Marinas
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190530120129.GD13751@fuggles.cambridge.arm.com \
--to=will.deacon@arm.com \
--cc=bigeasy@linutronix.de \
--cc=catalin.marinas@arm.com \
--cc=dave.martin@arm.com \
--cc=julien.grall@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rt-users@vger.kernel.org \
--cc=rostedt@goodmis.org \
--cc=suzuki.poulose@arm.com \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).