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SubjectRe: [PATCH] x86: pda_init: fix memory leak with CPU_HOTPLUG
On Fri, 1 Aug 2008 16:36:11 +0200 Andreas Herrmann <andreas.herrmann3@amd.com> wrote:

> pda->irqstackptr is allocated whenever a CPU is set online.
> But it is never freed (or did I miss something?).
> This results in a memory leak of 16 KByte for each CPU offline/online
> cycle.
>
> Fix is to allocate pda->irqstackptr only once.
>
> Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
> ---
> arch/x86/kernel/cpu/common_64.c | 15 +++++++++------
> 1 files changed, 9 insertions(+), 6 deletions(-)
>
> The leak is not a big deal for normal CPU hotplug usage.
> But when doing lots of CPU offline/online-cycles during stress tests
> this becomes significant.
>
> Patch is against Linus' git-tree (v2.6.27-rc1-157-gf164ca9).
>
>
> Regards,
>
> Andreas
>
> diff --git a/arch/x86/kernel/cpu/common_64.c b/arch/x86/kernel/cpu/common_64.c
> index dd6e3f1..c941397 100644
> --- a/arch/x86/kernel/cpu/common_64.c
> +++ b/arch/x86/kernel/cpu/common_64.c
> @@ -493,17 +493,20 @@ void pda_init(int cpu)
> /* others are initialized in smpboot.c */
> pda->pcurrent = &init_task;
> pda->irqstackptr = boot_cpu_stack;
> + pda->irqstackptr += IRQSTACKSIZE - 64;
> } else {
> - pda->irqstackptr = (char *)
> - __get_free_pages(GFP_ATOMIC, IRQSTACK_ORDER);
> - if (!pda->irqstackptr)
> - panic("cannot allocate irqstack for cpu %d", cpu);
> + if (!pda->irqstackptr) {
> + pda->irqstackptr = (char *)
> + __get_free_pages(GFP_ATOMIC, IRQSTACK_ORDER);
> + if (!pda->irqstackptr)
> + panic("cannot allocate irqstack for cpu %d",
> + cpu);
> + pda->irqstackptr += IRQSTACKSIZE - 64;
> + }
>
> if (pda->nodenumber == 0 && cpu_to_node(cpu) != NUMA_NO_NODE)
> pda->nodenumber = cpu_to_node(cpu);
> }
> -
> - pda->irqstackptr += IRQSTACKSIZE-64;
> }
>
> char boot_exception_stacks[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ +

It gives one the creeps seeing a trivially-triggerable panic() call in
a non-__init codepath.

And lo, one of pda_init's callers is __init and the other is __cpuinit.
So this function can at least be made __cpuinit().

But if we can still panic the kernel if a GFP_ATOMIC allocation fails
at cpu-hotplug time then that's still a problem.

cpu_init() has the same shortcoming.


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