On Tue, Mar 17, 2015 at 09:27:36AM +0100, Ingo Molnar wrote:
> Ok, in any case I'm doing a rebase of the affected commits in
> tip:x86/asm. That's a tree where we don't want to break bisectability,
> and this breakage looks sufficiently mysterious.
Yeah.
And it keeps getting better and better. I added some debug output to the
PF-path to see why exactly we segfault and the guest booted fine! No
segfaults. So add timing to that failure :-(
---
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index ede025fb46f1..54ca8539f345 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -746,6 +746,9 @@ show_signal_msg(struct pt_regs *regs, unsigned long
error_code,
print_vma_addr(KERN_CONT " in ", regs->ip);
printk(KERN_CONT "\n");
+
+ dump_stack();
+
}
static void
@@ -827,8 +830,10 @@ __bad_area(struct pt_regs *regs, unsigned long error_code,
}
static noinline void
-bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
+bad_area(const char *where, struct pt_regs *regs, unsigned long error_code,
+ unsigned long address)
{
+ pr_emerg("%s: %s\n", __func__, where);
__bad_area(regs, error_code, address, SEGV_MAPERR);
}
@@ -1189,13 +1194,13 @@ retry:
vma = find_vma(mm, address);
if (unlikely(!vma)) {
- bad_area(regs, error_code, address);
+ bad_area("!vma", regs, error_code, address);
return;
}
if (likely(vma->vm_start <= address))
goto good_area;
if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
- bad_area(regs, error_code, address);
+ bad_area("!VM_GROWSDOWN", regs, error_code, address);
return;
}
if (error_code & PF_USER) {
@@ -1206,12 +1211,12 @@ retry:
* 32 pointers and then decrements %sp by 65535.)
*/
if (unlikely(address + 65536 + 32 * sizeof(unsigned long) <
regs->sp)) {
- bad_area(regs, error_code, address);
+ bad_area("65536", regs, error_code, address);
return;
}
}
if (unlikely(expand_stack(vma, address))) {
- bad_area(regs, error_code, address);
+ bad_area("expand_stack", regs, error_code, address);
return;
}
diff --git a/mm/mmap.c b/mm/mmap.c
index da9990acc08b..47c4321f0d18 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2225,13 +2225,17 @@ int expand_downwards(struct vm_area_struct *vma,
* We must make sure the anon_vma is allocated
* so that the anon_vma locking is not a noop.
*/
- if (unlikely(anon_vma_prepare(vma)))
+ if (unlikely(anon_vma_prepare(vma))) {
+ pr_err("anon_vma_prepare\n");
return -ENOMEM;
+ }
address &= PAGE_MASK;
error = security_mmap_addr(address);
- if (error)
+ if (error) {
+ pr_err("security_mmap_addr\n");
return error;
+ }
vma_lock_anon_vma(vma);
@@ -2278,6 +2282,7 @@ int expand_downwards(struct vm_area_struct *vma,
vma_unlock_anon_vma(vma);
khugepaged_enter_vma_merge(vma, vma->vm_flags);
validate_mm(vma->vm_mm);
+ pr_err("validate_mm: %d\n", error);
return error;
}
@@ -2326,11 +2331,15 @@ int expand_stack(struct vm_area_struct *vma, unsigned
long address)
{
struct vm_area_struct *prev;
+ pr_err("%s: address: 0x%lx\n", __func__, address);
+
address &= PAGE_MASK;
prev = vma->vm_prev;
if (prev && prev->vm_end == address) {
- if (!(prev->vm_flags & VM_GROWSDOWN))
+ if (!(prev->vm_flags & VM_GROWSDOWN)) {
+ pr_err("!(prev->vm_flags & VM_GROWSDOWN)\n");
return -ENOMEM;
+ }
}
return expand_downwards(vma, address);
}
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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