On 8/7/07, Jan Kiszka <[EMAIL PROTECTED]> wrote:
> Gilles Chanteperdrix wrote:
> > On 8/7/07, Jan Kiszka <[EMAIL PROTECTED]> wrote:
> >> Gilles Chanteperdrix wrote:
> >>> Jan Kiszka wrote:
> >>>> Hi all,
> >>>>
> >>>> we are getting a lot of
> >>>>
> >>>> BUG: sleeping function called from invalid context at 
> >>>> mm/page_alloc.c:1225
> >>>> in_atomic():1, irqs_disabled():0
> >>>>  [<c010305d>] show_trace_log_lvl+0x1a/0x2f
> >>>>  [<c0103156>] show_trace+0x12/0x14
> >>>>  [<c0103915>] dump_stack+0x16/0x18
> >>>>  [<c010c4ab>] __might_sleep+0xcd/0xd3
> >>>>  [<c0149488>] __alloc_pages+0x32/0x281
> >>>>  [<c014fdd2>] copy_page_range+0x221/0x41e
> >>>>  [<c010ec18>] copy_process+0x9e1/0xfe2
> >>>>  [<c010f415>] do_fork+0x99/0x176
> >>>>  [<c0100e75>] sys_clone+0x33/0x39
> >>>>  [<c0102aaf>] syscall_call+0x7/0xb
> >>>>  =======================
> >>>>
> >>>> here due to a Xenomai program issuing system() calls.
> >>>>
> >>>> After once again dissecting the "nice" mm code (sigh...), the reason
> >>>> turned out to be plain simple:
> >>>>
> >>>> copy_pte_range(...);
> >>>>   spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
> >>>>   copy_one_pte(...);
> >>>>     if (is_cow_mapping(vm_flags))
> >>>>       alloc_page_vma(GFP_HIGHUSER, ...);
> >>>>         __alloc_pages(...)
> >>>>        might_sleep_if(gfp_mask & __GFP_WAIT);
> >>>>
> >>>> And this is true due to #define GFP_HIGHUSER (__GFP_WAIT | ...
> >>>>
> >>>> So the bad news is that the COW code in likely all i-pipe versions is
> >>>> broken. But the good new is that this might be easily fixable by
> >>>> providing the right gfp_mask. GFP_ATOMIC?
> >>> It does not look like a good solution, you are going to empty the
> >>> GFP_ATOMIC pools. The proper solution would rather be to look at the
> >>> real mm code (I mean not the one I wrote) and see how they cope with
> >>> this issue.
> >> Mmpf. What are the chances for a quick fix within the next days? We have
> >> to consider alternatives right now here because the whole system is
> >> meant for production purpose next week (C-ELROB '07).
> >>
> >> OK, I'm already finding myself inside the code :-/. What about this
> >> approach: We try to alloc with GFP_ATOMIC. Once this fails, we break
> >> out, drop all locks (just like it happens in case of need_resched()),
> >> try to fill up the pool, and restart then. What would reliably make
> >> Linux refill its atomic pool?
> >>
> >> Alternative approach: preallocate the required pages before entering the
> >> loop in copy_pte_range. But that may require more code changes.
> >
> > I would say the real fix is to drop momentarily the spinlock(s?) for 
> > allocating.
> >
>
> Are you sure it's safe to drop locks in the (logical) middle of
> copy_one_pte()? I can't tell yet from the few glances I took. It's just
> my feeling that says "no" so far.

There is certainly something possible, since the vanilla kernel
actually works without these warning.

-- 
                                               Gilles Chanteperdrix

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