Hi Tejun,
as we discussed, i include some discussion content in the commit message.
could you give some new comments or acknowledgment for this patch?
On 2016/9/30 19:30, zijun_hu wrote:
> From: zijun_hu <zijun...@htc.com>
>
> it will cause memory leakage for pcpu_embed_first_chunk() to go to
> label @out_free if the chunk spans over 3/4 VMALLOC area. all memory
> are allocated and recorded into array @areas for each CPU group, but
> the memory allocated aren't be freed before returning after going to
> label @out_free.
>
> in order to fix this bug, we check chunk spanned area immediately
> after completing memory allocation for all CPU group, we go to label
> @out_free_areas other than @out_free to free all memory allocated if
> the checking is failed.
>
> in order to verify the approach, we dump all memory allocated then
> enforce the jump then dump all memory freed, the result is okay after
> checking whether we free all memory we allocate in this function.
>
> BTW, The approach is chosen after thinking over the below scenes
> - we don't go to label @out_free directly to fix this issue since we
> maybe free several allocated memory blocks twice
> - the aim of jumping after pcpu_setup_first_chunk() is bypassing free
> usable memory other than handling error, moreover, the function does
> not return error code in any case, it either panics due to BUG_ON()
> or return 0.
>
> Signed-off-by: zijun_hu <zijun...@htc.com>
> Tested-by: zijun_hu <zijun...@htc.com>
> ---
> this patch is based on mmotm/linux-next branch so can be
> applied to them directly
>
> Changes in v2:
> - more detailed commit message is provided as discussed
> with t...@kernel.org
>
> mm/percpu.c | 36 ++++++++++++++++++------------------
> 1 file changed, 18 insertions(+), 18 deletions(-)
>
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 41d9d0b35801..7a5dae185ce1 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -1963,7 +1963,7 @@ int __init pcpu_embed_first_chunk(size_t reserved_size,
> size_t dyn_size,
> struct pcpu_alloc_info *ai;
> size_t size_sum, areas_size;
> unsigned long max_distance;
> - int group, i, rc;
> + int group, i, j, rc;
>
> ai = pcpu_build_alloc_info(reserved_size, dyn_size, atom_size,
> cpu_distance_fn);
> @@ -1979,7 +1979,8 @@ int __init pcpu_embed_first_chunk(size_t reserved_size,
> size_t dyn_size,
> goto out_free;
> }
>
> - /* allocate, copy and determine base address */
> + /* allocate, copy and determine base address & max_distance */
> + j = 0;
> for (group = 0; group < ai->nr_groups; group++) {
> struct pcpu_group_info *gi = &ai->groups[group];
> unsigned int cpu = NR_CPUS;
> @@ -2000,6 +2001,21 @@ int __init pcpu_embed_first_chunk(size_t
> reserved_size, size_t dyn_size,
> areas[group] = ptr;
>
> base = min(ptr, base);
> + if (ptr > areas[j])
> + j = group;
> + }
> + max_distance = areas[j] - base;
> + max_distance += ai->unit_size * ai->groups[j].nr_units;
> +
> + /* warn if maximum distance is further than 75% of vmalloc space */
> + if (max_distance > VMALLOC_TOTAL * 3 / 4) {
> + pr_warn("max_distance=0x%lx too large for vmalloc space
> 0x%lx\n",
> + max_distance, VMALLOC_TOTAL);
> +#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
> + /* and fail if we have fallback */
> + rc = -EINVAL;
> + goto out_free_areas;
> +#endif
> }
>
> /*
> @@ -2024,24 +2040,8 @@ int __init pcpu_embed_first_chunk(size_t
> reserved_size, size_t dyn_size,
> }
>
> /* base address is now known, determine group base offsets */
> - i = 0;
> for (group = 0; group < ai->nr_groups; group++) {
> ai->groups[group].base_offset = areas[group] - base;
> - if (areas[group] > areas[i])
> - i = group;
> - }
> - max_distance = ai->groups[i].base_offset +
> - (unsigned long)ai->unit_size * ai->groups[i].nr_units;
> -
> - /* warn if maximum distance is further than 75% of vmalloc space */
> - if (max_distance > VMALLOC_TOTAL * 3 / 4) {
> - pr_warn("max_distance=0x%lx too large for vmalloc space
> 0x%lx\n",
> - max_distance, VMALLOC_TOTAL);
> -#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
> - /* and fail if we have fallback */
> - rc = -EINVAL;
> - goto out_free;
> -#endif
> }
>
> pr_info("Embedded %zu pages/cpu @%p s%zu r%zu d%zu u%zu\n",
>
