Re: [Crash-utility] x86_64 limit of 454 cpu's?

----- Original Message ----- > (4/15/2011 09:04), Dave Anderson wrote: > > > > > > ----- Original Message ----- > >> Hi Dave, and company, > >> > >> I get this error trying to open a dump of a large system: > >> > >> crash: compressed kdump: invalid nr_cpus value: 640 > >> crash: vmcore: not a supported file format > >> > >> The message is from diskdump.c: > >> if (sizeof(*header) + sizeof(void *) * header->nr_cpus> block_size > >> || > >> header->nr_cpus<= 0) { > >> error(INFO, "%s: invalid nr_cpus value: %d\n", > >> > >> block_size is the page size of 4096 > >> struct disk_dump_header looks like 464 bytes > >> void * is 8 > >> So it looks like 454 is the maximum number of cpus. > >> 464 + 454*8 -> 4096 > >> > >> Is this intentional? > >> It looks like a restriction that no one ever complained about. But > >> there > >> are systems (Altix UV) with 2048 cpu's. > >> > >> Is there an easy fix? > >> > >> -Cliff > > > > To be honest, I don't know, I didn't design or write that code. > > Yes, this is intentional for RHEL4/diskdump. In the RHEL4 kernel, > disk_dump_header is defined as follows. > > struct disk_dump_header { > char signature[8]; /* = "DISKDUMP" */ > (snip) > int nr_cpus; /* Number of CPUs */ > struct task_struct *tasks[NR_CPUS]; > }; > > And maximum logical CPUs of RHEL4 are 32(x86) or 64(x86_64) so > this does not cause any problem. > > On the other hands, as you and Dave said, this causes limitation > problem > in RHEL5/RHEL6 kernel. But as far as I know, makedumpfile does not use > this "tasks" member, so we can skip here. > > if (is_diskdump?) > if (sizeof(*header) + sizeof(void *) * header->nr_cpus> block_size || > header->nr_cpus<= 0) { > error(INFO, "%s: invalid nr_cpus value: %d\n", > goto err; > } > > Something like this. Dave, Ohmichi-san, what do you think? > > Thanks, > Takao Indoh Looking at a couple sample compressed kdumps, it does appear that they do not set up the tasks[] array, and that the sub_header still starts at the "header->block_size". That being the case, your proposal looks like a nice, simple fix! Cliff, can you enclose that piece of code with something like: if (DISKDUMP_VALID()) { if (sizeof(*header) + sizeof(void *) * header->nr_cpus > block_size || header->nr_cpus <= 0) { error(INFO, "%s: invalid nr_cpus value: %d\n", DISKDUMP_VALID() ? "diskdump" : "compressed kdump", header->nr_cpus); goto err; } } I suppose it should still check for (header->nr_cpus <= 0), but I'll let Ken'ichi confirm that.

> > And you're right, although dumpfiles with that many cpus are highly > > unusual, but looking at the code, it certainly does appear that the > > disk_dump_header plus the task pointers for each cpu must fit in a > > "block_size", or page size, and that the sub_header is the first > > item > > following the contents of the first page: > > > > --- > > ^ disk_dump_header > > | task on cpu 0 > > page ... > > | task on cpu x-1 > > V task on cpu x > > --- > > sub_header > > bitmap > > remaining stuff... > > > > Since your dump is presumably a compressed kdump, I'm wondering > > what the makedumpfile code did in your case? Did it round up the > > location of the sub_header to a page boundary? > > > > I've cc'd this to Ken'ichi Ohmichi (makedumpfile), and to Takao > > Indoh > > (original compressed diskdump) for their input.