Hi Alex,
+cc kexec list (the right one for makedumpfile patch)
-----Original Message-----
> Whenever the variables compound_order or private become greater than
> 31, left bit-shift of 1 overflows, and nr_pages becomes zero. If nr_pages
> becomes 0 and pages are being excluded at the end of the PFN loop, the
> else branch of the last if statement is entered and pfn is decremented by
> 1 because nr_pages is 0. Finally, this causes the loop variable pfn to
> be assigned the same value as before when the next loop iteration begins
> which results in an infinite loop.
>
> This issue appeared on s390 64bit architecture with a dump of 16GB RAM.
The patch looks good to me, but just out of curiosity, when do the
compound_order or private become greater than 31 on s390?
Thanks,
Kazu
>
> This is a simple program to demonstrate the primary issue:
>
> void main(void)
> {
> unsigned long long n;
> unsigned long m;
>
> m = 32;
> n = 1 << m;
> fprintf(stderr, "%llx\n", n);
> n = 1UL << m;
> fprintf(stderr, "%llx\n", n);
> }
>
> Signed-off-by: Alexander Egorenkov <egorenar@xxxxxxxxxxxxx>
> ---
> makedumpfile.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/makedumpfile.c b/makedumpfile.c
> index c063267f15bb..863840b13608 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -6210,7 +6210,7 @@ __exclude_unnecessary_pages(unsigned long mem_map,
> if (OFFSET(page.private) != NOT_FOUND_STRUCTURE)
> private = ULONG(pcache + OFFSET(page.private));
>
> - nr_pages = 1 << compound_order;
> + nr_pages = 1UL << compound_order;
> pfn_counter = NULL;
>
> /*
> @@ -6227,7 +6227,7 @@ __exclude_unnecessary_pages(unsigned long mem_map,
> else if ((info->dump_level & DL_EXCLUDE_FREE)
> && info->page_is_buddy
> && info->page_is_buddy(flags, _mapcount, private, _count)) {
> - nr_pages = 1 << private;
> + nr_pages = 1UL << private;
> pfn_counter = &pfn_free;
> }
> /*
> --
> 2.31.1
>
> --
> Crash-utility mailing list
> Crash-utility@xxxxxxxxxx
> https://listman.redhat.com/mailman/listinfo/crash-utility
_______________________________________________
kexec mailing list
kexec@xxxxxxxxxxxxxxxxxxx
http://lists.infradead.org/mailman/listinfo/kexec
