lkml.org 
[lkml]   [2008]   [Jul]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/2] coredump: exit_mm: clear ->mm first, then play with ->core_state
On 07/19, Roland McGrath wrote:
>
> > With the previous changes the sub-threads which participate in coredump do
> > not need to have the valid ->mm when the coredump is in progress, now we
> > can decouple exit_mm() from coredumping code.
>
> I'm all for separating the code more cleanly. But I don't think it can
> work to change the order of the operations, i.e. it is not really true that
> core dumps don't need each thread's ->mm link to be valid. Is there a
> benefit to unlinking the mm before waiting for the core dump to finish?

If select_bad_process() sees the PF_EXITING task with ->mm != NULL, it
returns ERR_PTR(-1). This means that any prcoess doing the mt coredump
blocks oom kill completely. It is not that oom_kill doesn't take this
process into account, oom_kill just can't work intil ->core_dump()
completes.

Yes, oom_kill.c in turn need fixes but still this is not nice, and I
personally hate this coredump code in the middle of exit_mm().

However,

> The issue is that the user_regset calls to get "thread state" might
> actually read some user memory. Those calls use a task_struct pointer and
> you don't get to separately tell them the mm_struct describing the thread's
> address space. For example, the sparc64 "general registers" note for core
> files includes the register window read from user memory.
>
> So, it's not OK to clear the ->mm before everything examining the thread's
> machine state is really done, i.e. core dump and anything else.

Oh, thanks Roland.

Andrew, please drop

coredump-binfmt_elf_fdpic-dont-use-sub-threads-mm.patch
coredump-exit_mm-clear-mm-first-then-play-with-core_state.patch





btw, arch/sparc64/kernel/ptrace.c has a lot of

if (target == current)
copy_xxx_user();
else
access_process_vm();

perhaps it make sense to make a helper. Just curious (I don't know what
regset is), is it possible that ->get() is called when target->mm == NULL?

Oleg.



\
 
 \ /
  Last update: 2008-07-20 14:23    [W:1.038 / U:0.044 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site