if (in_atomic() || !mm) goto no_context;
/*
* As per x86, we may deadlock here. However, since the kernel only
* validly references user space from well defined areas of the code,
* we can bug out early if this is from code which shouldn't.
*/
if (!down_read_trylock(&mm->mmap_sem)) {
if (!user_mode(regs) && !search_exception_tables(regs->ARM_pc))
goto no_context;
down_read(&mm->mmap_sem);
} else {
/*
* The above down_read_trylock() might have succeeded in
* which case, we'll have missed the might_sleep() from
* down_read()
*/
might_sleep();
#ifdef CONFIG_DEBUG_VM
if (!user_mode(regs) &&
!search_exception_tables(regs->ARM_pc))
goto no_context;
#endif
}
fault = __do_page_fault(mm, addr, fsr, tsk);
up_read(&mm->mmap_sem);
/*
* Handle the "normal" case first - VM_FAULT_MAJOR / VM_FAULT_MINOR
*/
/*如果返回值fault不是这里面的值，那么应该会是VM_FAULT_MAJOR或VM_FAULT_MINOR，说明问题解决了，返回，一般正常情况下，__do_page_fault的返回值fault会是0(VM_FAULT_MINOR)或者其他一些值，都不是下面之后会看到的这些*/
if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP | VM_FAULT_BADACCESS))))
return 0;
/*如果fault是VM_FAULT_OOM这个级别的错误，那么这要杀掉进程*/
if (fault & VM_FAULT_OOM) {
/*
* We ran out of memory, call the OOM killer, and return to
* userspace (which will retry the fault, or kill us if we
* got oom-killed)
*/
pagefault_out_of_memory();
return 0;
}
/*
* If we are in kernel mode at this point, we
* have no context to handle this fault with.
*/
/*再次判断是否是内核空间出现了页异常，并且通过__do_page_fault没有没有解决，跳到到no_context*/
if (!user_mode(regs))
goto no_context;
/*下面两个情况，通过英文注释可以理解，
一个是无法修复，另一个是访问非法地址，都是要杀掉进程的错误*/
if (fault & VM_FAULT_SIGBUS) {
/*
* We had some memory, but were unable to
* successfully fix up this page fault.
*/
sig = SIGBUS;
code = BUS_ADRERR;
} else {
/*
* Something tried to access memory that
* isn't in our memory map..
*/
sig = SIGSEGV;
code = fault == VM_FAULT_BADACCESS ?
SEGV_ACCERR : SEGV_MAPERR;
}
/*给用户进程发送相应的信号，杀掉进程*/
__do_user_fault(tsk, addr, fsr, sig, code, regs);
return 0;
no_context:
/*内核引发的异常处理，如修复不畅，内核也要杀掉*/
__do_kernel_fault(mm, addr, fsr, regs);
return 0;
}
首先看第一个重点，源码片段如下：
/*1、判断当前是否是在原子操作中(中断、可延迟函数、临界区)发生的异常
2、通过mm是否存在判断是否是内核线程，对于内核线程，进程描述符的mm总为NULL，一旦成立，说明是在内核态中发生的异常，跳到标号no_context*/
if (in_atomic() || !mm)
goto no_context; |
