Commit fee7e49d4514 ("mm: propagate error from stack expansion even for guard page") made sure that we return the error properly for stack growth conditions. It also theorized that counting the guard page towards the stack limit might break something, but also said "Let's see if anybody notices". Somebody did notice. Apparently android-x86 sets the stack limit very close to the limit indeed, and including the guard page in the rlimit check causes the android 'zygote' process problems. So this adds the (fairly trivial) code to make the stack rlimit check be against the actual real stack size, rather than the size of the vma that includes the guard page.
Unified · Split
| @@ -2099,14 +2099,17 @@ static int acct_stack_growth(struct vm_area_struct *vma, unsigned long size, uns · 2098 unmodified lines | ||
| 2099 | 2099 | { |
| 2100 | 2100 | struct mm_struct *mm = vma->vm_mm; |
| 2101 | 2101 | struct rlimit *rlim = current->signal->rlim; |
| 2102 | − unsigned long new_start; | |
| 2102 | + unsigned long new_start, actual_size; | |
| 2103 | 2103 | |
| 2104 | 2104 | /* address space limit tests */ |
| 2105 | 2105 | if (!may_expand_vm(mm, grow)) |
| 2106 | 2106 | return -ENOMEM; |
| 2107 | 2107 | |
| 2108 | 2108 | /* Stack limit test */ |
| 2109 | − if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur)) | |
| 2109 | + actual_size = size; | |
| 2110 | + if (size && (vma->vm_flags & (VM_GROWSUP | VM_GROWSDOWN))) | |
| 2111 | + actual_size -= PAGE_SIZE; | |
| 2112 | + if (actual_size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur)) | |
| 2110 | 2113 | return -ENOMEM; |
| 2111 | 2114 | |
| 2112 | 2115 | /* mlock limit tests */ |