Re: [PATCH -tip 1/3] Pass mm->flags to binfmt core_dump for bitflagconsistency

From: Ingo Molnar
Date: Fri Nov 13 2009 - 18:23:38 EST



* Roland McGrath <roland@xxxxxxxxxx> wrote:

> To clarify, proc_coredump_filter_write() is the one place that can
> change mm->flags during a core dump. I don't think any other is
> possible while all the other tasks sharing that mm are prevented from
> running. Is there any other way that mm->flags might change during
> do_coredump()?
>
> I don't see anything wrong with this change. But (assuming that is
> the only case), there is another approach we could take instead. That
> is, have proc_coredump_filter_write() do:
>
> down_read(&mm->mmap_sem);
> ret = mm->core_state ? -EBUSY : 0;
> up_read(&mm->mmap_sem);

this would fix the (probably harmless) race too, but isnt the whole
approach taken by the patch more robust, i.e. to take a snapshot of
mm->flags value and pass it along coredump processing?

That makes it evidently immutable in the future too. It also makes the
code a bit easier to read IMO - instead of get_dumpable() we use the
mm_flags.

The only other observation i have is that for this parameter set:

long signr, struct pt_regs *regs, struct file *file,
unsigned long limit, unsigned long mm_flags)

we should probably introduce a coredump parameter struct, and pass that
along:

struct coredump_params {
long signr;
struct pt_regs *regs;
struct file *file;
unsigned long limit;
unsigned long mm_flags;
}

Had this been done in the past this present patch would be a lot simpler
as well: we could have added mm_flags to coredump_params, instead of
having to propagate it through ~6 function interface surfaces.

Thanks,

Ingo
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