linux-kernel - Re: [PATCH] PCI/AER: Check for NULL aer_info before ratelimiting in pci_print

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Message-ID: <umpfhbh2eufgryjzngc7kyvjlqf3d6fgzftgeb44yf4bbtizb6@x7iqbksbbcot>
Date: Wed, 6 Aug 2025 01:45:57 -0700
From: Breno Leitao <leitao@...ian.org>
To: Ethan Zhao <etzhao1900@...il.com>
Cc: Mahesh J Salgaonkar <mahesh@...ux.ibm.com>, 
	Oliver O'Halloran <oohall@...il.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>, Jon Pan-Doh <pandoh@...gle.com>, linuxppc-dev@...ts.ozlabs.org, 
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH] PCI/AER: Check for NULL aer_info before ratelimiting in
 pci_print_aer()

Hello Ethan,

On Wed, Aug 06, 2025 at 09:55:05AM +0800, Ethan Zhao wrote:
> On 8/4/2025 5:17 PM, Breno Leitao wrote:
> > Similarly to pci_dev_aer_stats_incr(), pci_print_aer() may be called
> > when dev->aer_info is NULL. Add a NULL check before proceeding to avoid
> > calling aer_ratelimit() with a NULL aer_info pointer, returning 1, which
> > does not rate limit, given this is fatal.
> > 
> > This prevents a kernel crash triggered by dereferencing a NULL pointer
> > in aer_ratelimit(), ensuring safer handling of PCI devices that lack
> > AER info. This change aligns pci_print_aer() with pci_dev_aer_stats_incr()
> > which already performs this NULL check.
> > 
> The enqueue side has lock to protect the ring, but the dequeue side no lock
> held.
> 
> The kfifo_get in
> static void aer_recover_work_func(struct work_struct *work)
> {
> ...
> while (kfifo_get(&aer_recover_ring, &entry)) {
> ...
> }
> should be replaced by
> kfifo_out_spinlocked()

The design seems not to need the lock on the reader side. There is just
one reader, which is the aer_recover_work. aer_recover_work runs
aer_recover_work_func(). So, if we just have one reader, we do not need
to protect the kfifo by spinlock, right?

In fact, the code documents it in the aer_recover_ring_lock.

	/*
	* Mutual exclusion for writers of aer_recover_ring, reader side don't
	* need lock, because there is only one reader and lock is not needed
	* between reader and writer.
	*/
	static DEFINE_SPINLOCK(aer_recover_ring_lock);