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. Jan
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