These are the same lines in my case. <readmem: c0d2af6c, KVADDR, "crash_notes", 4, (ROE), 85ba84c> <read_kdump: addr: c0d2af6c paddr: 80f2af6c cnt: 4> <readmem: f9fe0000, KVADDR, "note_buf_t", 560, (ROE), 85bac40> <--- !! <readmem: c0004000, KVADDR, "pgd page", 16384, (FOE), 914e8d0> I have never seen this problem before, so the behavior you see is exactly what I have seen before. However with a fairly new kernel I did not get the correct crash_notes. The investigation lead to the patch for the problem described in my previous mail. I have not investigated if there is any patch in newer kernels that changes this behavior and in that case where it comes from (it could be a patch by us). However as the algorithm for reading crash_notes is wrong, as it depends on a variable that is not yet initialized, I think it should be corrected anyhow. I have tested my patch with both newer and older kernels and it works as intended. Jan Jan Karlsson Senior Software Engineer MIB Sony Mobile Communications Tel: +46703062174 sonymobile.com -----Original Message----- From: crash-utility-bounces@xxxxxxxxxx [mailto:crash-utility-bounces@xxxxxxxxxx] On Behalf Of Dave Anderson Sent: onsdag den 18 juli 2012 15:13 To: Discussion list for crash utility usage, maintenance and development Cc: Fänge, Thomas Subject: Re: ARM: crash registers might be read from the wrong physical address ----- Original Message ----- > > > > > Hi Dave > > > > I found a problem in arm.c that arm_get_crash_notes() is called too > early. This has never been a problem until now. > > arm_get_crash_notes() in arm.c > calls readmem(, KVADDR, ) > which calls kvtop() > which calls machdep->kvtop that is arm_kvtop which uses > vt->vmalloc_start > vt->vmalloc_start is initialized in vm_init > > From main_loop: > > machdep_init(POST_GDB); > vm_init(); > machdep_init(POST_VM); > > arm_get_crash_notes() is currently called in the POST_GDB section of > machdep_init, but should be moved to the POST_VM section. I put the > comment and the code just before: > > if (init_unwind_tables()) { > > and then it works fine. Without this fix the crash registers might be > read from the wrong physical address. > > Jan Looking at the 2.6.38-based SMP ARM sample kernel I have, the arm_get_crash_notes() does not make any readmem() calls of a vmalloc address, only unity-mapped calls: $ crash -d7 vmlinux vmcore ... <readmem: c0b04230, KVADDR, "crash_notes", 4, (ROE), 85be9e0> <read_diskdump: addr: c0b04230 paddr: 80b04230 cnt: 4> <readmem: c0d5194c, KVADDR, "note_buf_t", 180, (ROE), 85bede0> <read_diskdump: addr: c0d5194c paddr: 80d5194c cnt: 180> ... Have newer ARM kernels changed how percpu addresses are translated such that the note_ptrs[] entries become vmalloc addresses here in arm_get_crash_notes():? if (symbol_exists("__per_cpu_offset")) { /* Add __per_cpu_offset for each cpu to form the pointer to the notes */ for (i = 0; i<kt->cpus; i++) notes_ptrs[i] = notes_ptrs[kt->cpus-1] + kt->__per_cpu_offset[i]; } Dave -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
