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Subject[PATCH 5.5 233/399] x86/nmi: Remove irq_work from the long duration NMI handler
Date
From: Changbin Du <changbin.du@gmail.com>

[ Upstream commit 248ed51048c40d36728e70914e38bffd7821da57 ]

First, printk() is NMI-context safe now since the safe printk() has been
implemented and it already has an irq_work to make NMI-context safe.

Second, this NMI irq_work actually does not work if a NMI handler causes
panic by watchdog timeout. It has no chance to run in such case, while
the safe printk() will flush its per-cpu buffers before panicking.

While at it, repurpose the irq_work callback into a function which
concentrates the NMI duration checking and makes the code easier to
follow.

[ bp: Massage. ]

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200111125427.15662-1-changbin.du@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/include/asm/nmi.h | 1 -
arch/x86/kernel/nmi.c | 20 +++++++++-----------
2 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h
index 75ded1d13d98d..9d5d949e662e1 100644
--- a/arch/x86/include/asm/nmi.h
+++ b/arch/x86/include/asm/nmi.h
@@ -41,7 +41,6 @@ struct nmiaction {
struct list_head list;
nmi_handler_t handler;
u64 max_duration;
- struct irq_work irq_work;
unsigned long flags;
const char *name;
};
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index e676a9916c498..54c21d6abd5ac 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -104,18 +104,22 @@ static int __init nmi_warning_debugfs(void)
}
fs_initcall(nmi_warning_debugfs);

-static void nmi_max_handler(struct irq_work *w)
+static void nmi_check_duration(struct nmiaction *action, u64 duration)
{
- struct nmiaction *a = container_of(w, struct nmiaction, irq_work);
+ u64 whole_msecs = READ_ONCE(action->max_duration);
int remainder_ns, decimal_msecs;
- u64 whole_msecs = READ_ONCE(a->max_duration);
+
+ if (duration < nmi_longest_ns || duration < action->max_duration)
+ return;
+
+ action->max_duration = duration;

remainder_ns = do_div(whole_msecs, (1000 * 1000));
decimal_msecs = remainder_ns / 1000;

printk_ratelimited(KERN_INFO
"INFO: NMI handler (%ps) took too long to run: %lld.%03d msecs\n",
- a->handler, whole_msecs, decimal_msecs);
+ action->handler, whole_msecs, decimal_msecs);
}

static int nmi_handle(unsigned int type, struct pt_regs *regs)
@@ -142,11 +146,7 @@ static int nmi_handle(unsigned int type, struct pt_regs *regs)
delta = sched_clock() - delta;
trace_nmi_handler(a->handler, (int)delta, thishandled);

- if (delta < nmi_longest_ns || delta < a->max_duration)
- continue;
-
- a->max_duration = delta;
- irq_work_queue(&a->irq_work);
+ nmi_check_duration(a, delta);
}

rcu_read_unlock();
@@ -164,8 +164,6 @@ int __register_nmi_handler(unsigned int type, struct nmiaction *action)
if (!action->handler)
return -EINVAL;

- init_irq_work(&action->irq_work, nmi_max_handler);
-
raw_spin_lock_irqsave(&desc->lock, flags);

/*
--
2.20.1


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