Re: [Crash-utility] mm_struct for exiting tasks
----- Original Message -----
Hello,
I'm Justin Vreeland, I'm currently and intern at Cray working with the
OS/Kernel group. We use crash frequently to track down various problems
and sometimes we need to get information about tasks that were exiting
when the dump was taken. Because the mm_struct has been removed from
the task struct. Crash doesn't let you use vtop or vm to do this so I
added a way to specify mm_struct (with -M) for tasks whose stats is
'Exiting'.
Currently it's a bit hackish it modifies the tasks status and context to
pass all the checks, and then restores both before returning. If this
is something you're interested in it I'd be happy to bring it up to
snuff. Modifications are attached.
--
-Justin
Hello Justin,
Welcome to the group...
Upon an initial glance, there are a few issues that make this
patch unpalatable.
It advertises the capability of forcing an mm_struct address, but gives
no clue has to how you would determine what the mm_struct address was?
Do you somehow verify that the mm_struct has not been freed by the final
mmput() at the end of exit_mm()?
static void exit_mm(struct task_struct * tsk)
{
...
task_lock(tsk);
tsk->mm = NULL;
up_read(&mm->mmap_sem);
enter_lazy_tlb(mm, current);
task_unlock(tsk);
mm_update_next_owner(mm);
mmput(mm);
}
Aside from that, I do have a problem with changing the prototypes of
functions advertised in defs.h, because they may be used by external
extension modules, and this would break users of vm_area_dump() or
IN_TASK_VMA().
And if the command were to fail while executing, the restoration
code would not run, leaving the task's data in the invalid/modified
state. (There is a command-cleanup facility that could be used, but
this would be the first/only time where valid kernel data is being
modified, which really bothers me...)
That all being said, I don't have a well-thought-out alternative
suggestion -- other than perhaps you can roll your own extension
module, that contains modified/stripped-down versions of vm_area_dump()
and vm_area_page_dump(), where you create your own task_context
structure -- and whatever else is required -- to accomplish the
same result.
Dave