RE: [PATCH v3 4/4] PCI: hv: Avoid a kmemleak false positive caused by the hbus buffer

[Michael Kelley <mikelley@microsoft.com>]

From: Dexuan Cui <decui@microsoft.com> Sent: Sunday, November 24, 2019 9:34 PM
> 
> With the recent 59bb47985c1d ("mm, sl[aou]b: guarantee natural
> alignment for kmalloc(power-of-two)"), kzalloc() is able to allocate
> a 4KB buffer that is guaranteed to be 4KB-aligned. Here the size and
> alignment of hbus is important because hbus's field
> retarget_msi_interrupt_params must not cross a 4KB page boundary.
> 
> Here we prefer kzalloc to get_zeroed_page(), because a buffer
> allocated by the latter is not tracked and scanned by kmemleak, and
> hence kmemleak reports the pointer contained in the hbus buffer
> (i.e. the hpdev struct, which is created in new_pcichild_device() and
> is tracked by hbus->children) as memory leak (false positive).
> 
> If the kernel doesn't have 59bb47985c1d, get_zeroed_page() *must* be
> used to allocate the hbus buffer and we can avoid the kmemleak false
> positive by using kmemleak_alloc() and kmemleak_free() to ask
> kmemleak to track and scan the hbus buffer.
> 
> Reported-by: Lili Deng <v-lide@microsoft.com>
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> ---
>  drivers/pci/controller/pci-hyperv.c | 24 +++++++++++++++++++++---
>  1 file changed, 21 insertions(+), 3 deletions(-)
> 

Reviewed-by: Michael Kelley <mikelley@microsoft.com>