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.
--
Gilles Chanteperdrix
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