linux-kernel - Re: [PATCH] PCI: Add missing lockdep assertion in pci_cfg_access

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Date: Tue, 04 Jun 2024 16:23:01 +0200
From: Niklas Schnelle <schnelle@...ux.ibm.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
        Dan Williams
 <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Matthew Rosato
	 <mjrosato@...ux.ibm.com>
Subject: Re: [PATCH] PCI: Add missing lockdep assertion in
 pci_cfg_access_trylock()

On Tue, 2024-06-04 at 15:38 +0200, Niklas Schnelle wrote:
> In commit 7e89efc6e9e4 ("PCI: Lock upstream bridge for
> pci_reset_function()") it was missed that pci_cfg_access_trylock() needs
> the same lockdep assertion as pci_cfg_access_lock(). This leads to false
> positive lockdep splats for users of pci_cfg_access_trylock(). Add the
> missing assertion when the lock was successfully acquired.
> 
> Fixes: 7e89efc6e9e4 ("PCI: Lock upstream bridge for pci_reset_function()")
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> ---
>  drivers/pci/access.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index 30f031de9cfe..5b6620da30d7 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -319,6 +319,8 @@ bool pci_cfg_access_trylock(struct pci_dev *dev)
>  		dev->block_cfg_access = 1;
>  	raw_spin_unlock_irqrestore(&pci_lock, flags);
>  
> +	if (locked)
> +		lock_map_acquire(&dev->cfg_access_lock);
>  	return locked;
>  }
>  EXPORT_SYMBOL_GPL(pci_cfg_access_trylock);
> 
> ---
> base-commit: c3f38fa61af77b49866b006939479069cd451173
> change-id: 20240604-pci_cfg_lockdep-b6914e62d726
> 
> Best regards,

Matt just pointed out to me that the same issue is also discussed with
a proposed fix in the discussion of the fixed commit[0]. That
additionally moves the lockdep asserts into the pci_lock critical
section.

[0]
https://lore.kernel.org/all/20240523153839.16102e26.alex.williamson@redhat.com/