On 01/02/24 at 10:49pm, Yuntao Wang wrote:
> The purpose of crash_exclude_mem_range() is to remove all memory ranges
> that overlap with [mstart-mend]. However, the current logic only removes
> the first overlapping memory range.
>
> Commit a2e9a95d2190 ("kexec: Improve & fix crash_exclude_mem_range() to
> handle overlapping ranges") attempted to address this issue, but it did not
> fix all error cases.
>
> Let's fix and simplify the logic of crash_exclude_mem_range().
Thanks, this makes the code logic much clearer and easier to follow.
Acked-by: Baoquan He <bhe@xxxxxxxxxx>
>
> Signed-off-by: Yuntao Wang <ytcoode@xxxxxxxxx>
> ---
> kernel/crash_core.c | 80 ++++++++++++++++-----------------------------
> 1 file changed, 29 insertions(+), 51 deletions(-)
>
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index efe87d501c8c..c51d0a54296b 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -565,9 +565,8 @@ int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
> int crash_exclude_mem_range(struct crash_mem *mem,
> unsigned long long mstart, unsigned long long mend)
> {
> - int i, j;
> + int i;
> unsigned long long start, end, p_start, p_end;
> - struct range temp_range = {0, 0};
>
> for (i = 0; i < mem->nr_ranges; i++) {
> start = mem->ranges[i].start;
> @@ -575,72 +574,51 @@ int crash_exclude_mem_range(struct crash_mem *mem,
> p_start = mstart;
> p_end = mend;
>
> - if (mstart > end || mend < start)
> + if (p_start > end)
> continue;
>
> + /*
> + * Because the memory ranges in mem->ranges are stored in
> + * ascending order, when we detect `p_end < start`, we can
> + * immediately exit the for loop, as the subsequent memory
> + * ranges will definitely be outside the range we are looking
> + * for.
> + */
> + if (p_end < start)
> + break;
> +
> /* Truncate any area outside of range */
> - if (mstart < start)
> + if (p_start < start)
> p_start = start;
> - if (mend > end)
> + if (p_end > end)
> p_end = end;
>
> /* Found completely overlapping range */
> if (p_start == start && p_end == end) {
> - mem->ranges[i].start = 0;
> - mem->ranges[i].end = 0;
> - if (i < mem->nr_ranges - 1) {
> - /* Shift rest of the ranges to left */
> - for (j = i; j < mem->nr_ranges - 1; j++) {
> - mem->ranges[j].start =
> - mem->ranges[j+1].start;
> - mem->ranges[j].end =
> - mem->ranges[j+1].end;
> - }
> -
> - /*
> - * Continue to check if there are another overlapping ranges
> - * from the current position because of shifting the above
> - * mem ranges.
> - */
> - i--;
> - mem->nr_ranges--;
> - continue;
> - }
> + memmove(&mem->ranges[i], &mem->ranges[i + 1],
> + (mem->nr_ranges - (i + 1)) * sizeof(mem->ranges[i]));
> + i--;
> mem->nr_ranges--;
> - return 0;
> - }
> -
> - if (p_start > start && p_end < end) {
> + } else if (p_start > start && p_end < end) {
> /* Split original range */
> + if (mem->nr_ranges >= mem->max_nr_ranges)
> + return -ENOMEM;
> +
> + memmove(&mem->ranges[i + 2], &mem->ranges[i + 1],
> + (mem->nr_ranges - (i + 1)) * sizeof(mem->ranges[i]));
> +
> mem->ranges[i].end = p_start - 1;
> - temp_range.start = p_end + 1;
> - temp_range.end = end;
> + mem->ranges[i + 1].start = p_end + 1;
> + mem->ranges[i + 1].end = end;
> +
> + i++;
> + mem->nr_ranges++;
> } else if (p_start != start)
> mem->ranges[i].end = p_start - 1;
> else
> mem->ranges[i].start = p_end + 1;
> - break;
> - }
> -
> - /* If a split happened, add the split to array */
> - if (!temp_range.end)
> - return 0;
> -
> - /* Split happened */
> - if (i == mem->max_nr_ranges - 1)
> - return -ENOMEM;
> -
> - /* Location where new range should go */
> - j = i + 1;
> - if (j < mem->nr_ranges) {
> - /* Move over all ranges one slot towards the end */
> - for (i = mem->nr_ranges - 1; i >= j; i--)
> - mem->ranges[i + 1] = mem->ranges[i];
> }
>
> - mem->ranges[j].start = temp_range.start;
> - mem->ranges[j].end = temp_range.end;
> - mem->nr_ranges++;
> return 0;
> }
>
> --
> 2.43.0
>
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