Re: [PATCH v3 1/1] PCI/IOV: Add reentrant locking in sriov_add_vfs/sriov_del_vfs for complete serialization

[Benjamin Block]

On Wed, Feb 25, 2026 at 10:24:34PM +0200, ionut.nechita@xxxxxxxxxxxxx wrote:
> From: Ionut Nechita <ionut.nechita@xxxxxxxxxxxxx>
> 
--8<--
> 
> Instead, introduce owner tracking for pci_rescan_remove_lock via a new
> pci_lock_rescan_remove_reentrant() helper. This function checks if the
> current task already holds the lock:
>  - If the lock is not held: acquires it and returns true, providing
>    full serialization against concurrent hotplug events (including
>    platform-generated events on s390).
>  - If the lock is already held by the current task (reentrant call from
>    remove_store or sriov_numvfs_store paths): returns false without
>    re-acquiring, avoiding deadlock while the caller already provides
>    the necessary serialization.
>  - If the lock is held by another task (concurrent hotplug): blocks
>    until the lock is released, then acquires it, providing complete
>    serialization. This is the key improvement over a trylock approach.
> 
--8<--
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index bccc7a4bdd794..467362c277f19 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -3509,19 +3509,38 @@ EXPORT_SYMBOL_GPL(pci_rescan_bus);
>   * routines should always be executed under this mutex.
>   */
>  DEFINE_MUTEX(pci_rescan_remove_lock);
> +static struct task_struct *pci_rescan_remove_owner;
                            ^
                            const *pci_rescan_remove_owner

Minor nitpick: you could declare this `const`; making it clear that this is
not meant to be used to modify the task in any way.

>  void pci_lock_rescan_remove(void)
>  {
>  	mutex_lock(&pci_rescan_remove_lock);
> +	pci_rescan_remove_owner = current;
>  }
>  EXPORT_SYMBOL_GPL(pci_lock_rescan_remove);
>  
>  void pci_unlock_rescan_remove(void)
>  {
> +	pci_rescan_remove_owner = NULL;
>  	mutex_unlock(&pci_rescan_remove_lock);
>  }
>  EXPORT_SYMBOL_GPL(pci_unlock_rescan_remove);
>  
> +bool pci_lock_rescan_remove_reentrant(void)
> +{
> +	if (pci_rescan_remove_owner == current)
> +		return false;
> +	pci_lock_rescan_remove();
> +	return true;
> +}
> +EXPORT_SYMBOL_GPL(pci_lock_rescan_remove_reentrant);

Otherwise this looks good to me.

I've run tests on s390 with hot-unplug from within Linux and externally
triggered, driver unbind/unload, s390 PCI recovery, and some other minor
tests.
No lockdep splats, no other warnings/splats; it looks good to me.


Reviewed-by: Benjamin Block <bblock@xxxxxxxxxxxxx>
Tested-by: Benjamin Block <bblock@xxxxxxxxxxxxx>

-- 
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