linux-kernel - [PATCH 04/30] firmware: google: Convert regular spinlock into trylock on panic path

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Date:   Wed, 27 Apr 2022 19:48:58 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     akpm@...ux-foundation.org, bhe@...hat.com, pmladek@...e.com,
        kexec@...ts.infradead.org
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        jgross@...e.com, john.ogness@...utronix.de, keescook@...omium.org,
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        paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, stern@...land.harvard.edu,
        tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com,
        will@...nel.org, Ard Biesheuvel <ardb@...nel.org>,
        David Gow <davidgow@...gle.com>,
        Evan Green <evgreen@...omium.org>,
        Julius Werner <jwerner@...omium.org>
Subject: [PATCH 04/30] firmware: google: Convert regular spinlock into trylock on panic path

Currently the gsmi driver registers a panic notifier as well as
reboot and die notifiers. The callbacks registered are called in
atomic and very limited context - for instance, panic disables
preemption, local IRQs and all other CPUs that aren't running the
current panic function.

With that said, taking a spinlock in this scenario is a
dangerous invitation for a deadlock scenario. So, we fix
that in this commit by changing the regular spinlock with
a trylock, which is a safer approach.

Fixes: 74c5b31c6618 ("driver: Google EFI SMI")
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: David Gow <davidgow@...gle.com>
Cc: Evan Green <evgreen@...omium.org>
Cc: Julius Werner <jwerner@...omium.org>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
---
 drivers/firmware/google/gsmi.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/google/gsmi.c b/drivers/firmware/google/gsmi.c
index adaa492c3d2d..b01ed02e4a87 100644
--- a/drivers/firmware/google/gsmi.c
+++ b/drivers/firmware/google/gsmi.c
@@ -629,7 +629,10 @@ static int gsmi_shutdown_reason(int reason)
 	if (saved_reason & (1 << reason))
 		return 0;
 
-	spin_lock_irqsave(&gsmi_dev.lock, flags);
+	if (!spin_trylock_irqsave(&gsmi_dev.lock, flags)) {
+		rc = -EBUSY;
+		goto out;
+	}
 
 	saved_reason |= (1 << reason);
 
@@ -646,6 +649,7 @@ static int gsmi_shutdown_reason(int reason)
 
 	spin_unlock_irqrestore(&gsmi_dev.lock, flags);
 
+out:
 	if (rc < 0)
 		printk(KERN_ERR "gsmi: Log Shutdown Reason failed\n");
 	else
-- 
2.36.0