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 _______________________________________________ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core