Messages in this thread | | | Date | Tue, 24 Apr 2012 16:19:47 +0900 | From | Minchan Kim <> | Subject | Re: [RFC] propagate gfp_t to page table alloc functions |
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On 04/24/2012 03:13 PM, Nick Piggin wrote:
> 2012/4/24 Minchan Kim <minchan@kernel.org>: >> On 04/24/2012 02:16 PM, KAMEZAWA Hiroyuki wrote: >> >>> (2012/04/23 17:55), Minchan Kim wrote: >>> >>>> As I test some code, I found a problem about deadlock by lockdep. >>>> The reason I saw the message is __vmalloc calls map_vm_area which calls >>>> pud/pmd_alloc without gfp_t. so although we call __vmalloc with >>>> GFP_ATOMIC or GFP_NOIO, it ends up allocating pages with GFP_KERNEL. >>>> The should be a BUG. This patch fixes it by passing gfp_to to low page >>>> table allocate functions. >>>> >>>> Signed-off-by: Minchan Kim <minchan@kernel.org> >>> >>> >>> Hmm ? vmalloc should support GFP_ATOMIC ? >> >> >> I'm not sure but alloc_large_system_hash already has used. >> And it's not specific on GFP_ATOMIC. >> We have to care of GFP_NOFS and GFP_NOIO to prevent deadlock on reclaim >> context. >> There are some places to use GFP_NOFS and we don't emit any warning >> message in case of that. > > What's the lockdep warning?
It's just some private-test code, not-mainlined and lockdep warning is like this.
[ INFO: inconsistent lock state ] 3.4.0-rc3-next-20120417+ #80 Not tainted --------------------------------- inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-R} usage.
It seems test code calls vmalloc inside reclaim context so that it enters reclaim context, again by map_vm_area which allocates pages with GFP_KERNEL.
Of course, I can avoid this problem by fixing the caller but during I look into this problem, found other places to use gfp_t with "context restriction".
>
> vmalloc was never supposed to use gfp flags for allocation "context" > restriction. I.e., it > was always supposed to have blocking, fs, and io capable allocation > context. The flags > were supposed to be a memory type modifier.
You mean "zone modifiers"?
> > These different classes of flags is a bit of a problem and source of > confusion we have. > We should be doing more checks for them, of course.
It might need some warning in __vmalloc and family which use gfp_t if the caller use context flags.
> > I suspect you need to fix the caller?
Hmm, there are several places to use GFP_NOIO and GFP_NOFS even, GFP_ATOMIC. I believe it's not trivial now.
> > Thanks, > Nick > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. 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@kvack.org"> email@kvack.org </a> >
-- Kind regards, Minchan Kim
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