On 04/28/2012 07:00 AM, Andrew Morton wrote: > On Fri, 27 Apr 2012 17:42:24 +0900 > Minchan Kim <minchan@xxxxxxxxxx> wrote: > >> Now there are several places to use __vmalloc with GFP_ATOMIC, >> GFP_NOIO, GFP_NOFS but unfortunately __vmalloc calls map_vm_area >> which calls alloc_pages with GFP_KERNEL to allocate page tables. >> It means it's possible to happen deadlock. >> I don't know why it doesn't have reported until now. >> >> Firstly, I tried passing gfp_t to lower functions to support __vmalloc >> with such flags but other mm guys don't want and decided that >> all of caller should be fixed. >> >> http://marc.info/?l=linux-kernel&m=133517143616544&w=2 >> >> To begin with, let's listen other's opinion whether they can fix it >> by other approach without calling __vmalloc with such flags. >> >> So this patch adds warning to detect and to be fixed hopely. >> I Cced related maintainers. >> If I miss someone, please Cced them. >> >> side-note: >> I added WARN_ON instead of WARN_ONCE to detect all of callers >> and each WARN_ON for each flag to detect to use any flag easily. >> After we fix all of caller or reduce such caller, we can merge >> a warning with WARN_ONCE. > > Just WARN_ONCE, please. If that exposes some sort of calamity then we > can reconsider. NP. > >> >> ... >> >> --- a/mm/vmalloc.c >> +++ b/mm/vmalloc.c >> @@ -1700,6 +1700,15 @@ static void *__vmalloc_node(unsigned long size, unsigned long align, >> gfp_t gfp_mask, pgprot_t prot, >> int node, void *caller) >> { >> + /* >> + * This function calls map_vm_area so that it allocates >> + * page table with GFP_KERNEL so caller should avoid using >> + * GFP_NOIO, GFP_NOFS and !__GFP_WAIT. >> + */ >> + WARN_ON(!(gfp_mask & __GFP_WAIT)); >> + WARN_ON(!(gfp_mask & __GFP_IO)); >> + WARN_ON(!(gfp_mask & __GFP_FS)); >> + >> return __vmalloc_node_range(size, align, VMALLOC_START, VMALLOC_END, >> gfp_mask, prot, node, caller); >> } > > This seems strange. There are many entry points to this code and the > patch appears to go into a randomly-chosen middle point in the various > call chains and sticks a check in there. Why was __vmalloc_node() > chosen? Does this provide full coverage or all entry points? I think it covers all of caller with calls __vmalloc with gfp_flags. Only exception is __vmalloc_node_range which is called by module_alloc but it surely calls __vmalloc_node_range with GFP_KERNEL so it's no problem now. If you want to catch potential use of __vmalloc_node_range in future, I can move it to it. > > > > Also, the patch won't warn in the most problematic cases such as > vmalloc() being called from a __GFP_NOFS context. Presumably there are I agree but this patch's goal is just to prevent calling __vmalloc with GFP_ATOMIC, GFP_NOFS and GFP_NOIO. We should consider vmalloc on __GFP_NOFS context as another problem and maybe reclaimfs lockdep would be a good start point. > might_sleep() warnings somewhere on the allocation path which will > catch vmalloc() being called from atomic contexts. Yes. > > I'm not sure what to do about that - we don't have machinery in place > to be able to detect when a GFP_KERNEL allocation is deadlockable. > Perhaps a lot of hacking on lockdep might get us this - we'd need to > teach lockdep about which locks prohibit FS entry, which locks prevent > IO entry, etc. And there are secret locks such as ext3/4 > journal_start(), and bitlocks and lock_page(). eek. > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>