Messages in this thread | | | From | David Howells <> | Subject | Re: [patch] remove MAX_ARG_PAGES | Date | Tue, 02 Jan 2007 18:18:48 +0000 |
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Ingo Molnar <mingo@elte.hu> wrote:
> FYI, i have forward ported your MAX_ARG_PAGES limit removal patch to > 2.6.20-rc2 and have included it in the -rt kernel. It's working great - > i can now finally do a "ls -t patches/*.patch" in my patch repository - > something i havent been able to do for years ;-)
I get a NULL kernel pointer reference with this patch with FRV in MMU mode. It's whilst the kernel is attempting to execute init:
(gdb) bt #0 0xc0063d54 in do_anonymous_page (mm=0xc05c1a04, vma=0xc05c884c, address=3221225457, page_table=0xdc00bffc, pmd=0xc05c6f00, write_access=0) at pgtable.h:525 #1 0xc006468c in __handle_mm_fault (mm=0xbffffff1, vma=0xc05c884c, address=3691036668, write_access=1) at memory.c:2404 #2 0xc0061c18 in get_user_pages (tsk=0xc034eba0, mm=0xc05c1a04, start=3221225457, len=1, write=1, force=0, pages=0xc0353b80, vmas=0x0) at memory.c:1064 #3 0xc0084c7c in copy_strings (argc=0, argv=0xc0388c3c, bprm=0xc0388b88) at exec.c:326 #4 0xc0084dac in copy_strings_kernel (argc=1, argv=0xc05c884c, bprm=0xbffffff1) at exec.c:365 #5 0xc0085f5c in do_execve (filename=0xc0387000 "/sbin/init", argv=0xc026e8c8, envp=0xc026e950, regs=0xc0353bf8) at exec.c:1158 #6 0xc000f55c in sys_execve (name=0x1 <Address 0x1 out of bounds>, argv=0xc026e8c8, envp=0xc026e950) at process.c:263 #7 0xc000e1e0 in __syscall_call () at arch/frv/kernel/entry.S:878 #8 0xc000e1e0 in __syscall_call () at arch/frv/kernel/entry.S:878
The problem appears to be that current->mm is NULL. It's a bit difficult to say for sure because gdb or gcc determined that the error is in pgtable.h, but doesn't seem to have determined which one.
However, looking at the code, I think it must be this:
static int do_anonymous_page(struct mm_struct *mm, ...) { ... update_mmu_cache(vma, address, entry); ... }
But that uses current->mm, which is NULL, via this function:
[include/asm-frv/pgtable.h]
/* * preload information about a newly instantiated PTE into the SCR0/SCR1 PGE cache */
static inline void update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t pte) { unsigned long ampr; pgd_t *pge = pgd_offset(current->mm, address); pud_t *pue = pud_offset(pge, address); pmd_t *pme = pmd_offset(pue, address);
ampr = pme->ste[0] & 0xffffff00; ampr |= xAMPRx_L | xAMPRx_SS_16Kb | xAMPRx_S | xAMPRx_C | xAMPRx_V;
asm volatile("movgs %0,scr0\n" "movgs %0,scr1\n" "movgs %1,dampr4\n" "movgs %1,dampr5\n" : : "r"(address), "r"(ampr) ); }
This really oughtn't to be called in this situation, I suspect. I could just skip the operation if current->mm is NULL, but I'm not sure that that's the right thing to do. Maybe I should be using current->active_mm instead.
Everything works fine without the patch.
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