Re: [PATCH 1/1] genirq: Properly pair kobject_del with kobject_add

gregkh
2019-08-02T06:34:28Z

On Thu, Aug 01, 2019 at 11:53:53PM +0000, Michael Kelley wrote:
> If alloc_descs fails before irq_sysfs_init has run, free_desc in the
> cleanup path will call kobject_del even though the kobject has not
> been added with kobject_add. Fix this by making the call to
> kobject_del conditional on whether irq_sysfs_init has run.
>
> This problem surfaced because commit aa30f47cf666
> ("kobject: Add support for default attribute groups to kobj_type")
> makes kobject_del stricter about pairing with kobject_add. If the
> pairing is incorrrect, a WARNING and backtrace occur in
> sysfs_remove_group because there is no parent.
>
> Fixes: ecb3f394c5db ("genirq: Expose interrupt information through sysfs")
> Signed-off-by: Michael Kelley <mikelley@microsoft.com>
> ---
> kernel/irq/irqdesc.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
> index 9484e88..5447760 100644
> --- a/kernel/irq/irqdesc.c
> +++ b/kernel/irq/irqdesc.c
> @@ -438,7 +438,8 @@ static void free_desc(unsigned int irq)
> * The sysfs entry must be serialized against a concurrent
> * irq_sysfs_init() as well.
> */
> - kobject_del(&desc->kobj);
> + if (irq_kobj_base)
> + kobject_del(&desc->kobj);

But now you leak the memory of desc as there is no chance it could be
freed, because the kobject release function is never called :(

Relying on irq_kobj_bas to be present or not seems like an odd test
here.

thanks,

greg k-h