Messages in this thread | | | Subject | Re: [PATCH] mm: fix invalid node in alloc_migrate_target() | From | Vlastimil Babka <> | Date | Fri, 1 Apr 2016 10:42:52 +0200 |
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On 03/31/2016 11:01 PM, Andrew Morton wrote: > On Thu, 31 Mar 2016 15:13:41 +0200 Vlastimil Babka <vbabka@suse.cz> wrote: > >> On 03/29/2016 03:06 PM, Vlastimil Babka wrote: >> > On 03/25/2016 08:22 PM, Andrew Morton wrote: >> >> Also, mm/mempolicy.c:offset_il_node() worries me: >> >> >> >> do { >> >> nid = next_node(nid, pol->v.nodes); >> >> c++; >> >> } while (c <= target); >> >> >> >> Can't `nid' hit MAX_NUMNODES? >> > >> > AFAICS it can. interleave_nid() uses this and the nid is then used e.g. >> > in node_zonelist() where it's used for NODE_DATA(nid). That's quite >> > scary. It also predates git. Why don't we see crashes or KASAN finding this? >> >> Ah, I see. In offset_il_node(), nid is initialized to -1, and the number >> of do-while iterations calling next_node() is up to the number of bits >> set in the pol->v.nodes bitmap, so it can't reach past the last set bit >> and return MAX_NUMNODES. > > Gack. offset_il_node() should be dragged out, strangled, shot then burnt.
Ah, but you went with the much less amusing alternative of just fixing it.
> static unsigned offset_il_node(struct mempolicy *pol, > struct vm_area_struct *vma, unsigned long off) > { > unsigned nnodes = nodes_weight(pol->v.nodes); > unsigned target; > int c; > int nid = NUMA_NO_NODE; > > if (!nnodes) > return numa_node_id(); > target = (unsigned int)off % nnodes; > c = 0; > do { > nid = next_node(nid, pol->v.nodes); > c++; > } while (c <= target); > return nid; > } > > For starters it is relying upon next_node(-1, ...) behaving like > first_node(). Fair enough I guess, but that isn't very clear. > > static inline int __next_node(int n, const nodemask_t *srcp) > { > return min_t(int,MAX_NUMNODES,find_next_bit(srcp->bits, MAX_NUMNODES, n+1)); > } > > will start from node 0 when it does the n+1. > > Also it is relying upon NUMA_NO_NODE having a value of -1. That's just > grubby - this code shouldn't "know" that NUMA_NO_NODE==-1. It would have > been better to use plain old "-1" here.
Yeah looks like a blind change of all "-1" to "NUMA_NO_NODE" happened at some point.
> > Does this look clearer and correct?
Definitely.
> /* > * Do static interleaving for a VMA with known offset @n. Returns the n'th > * node in pol->v.nodes (starting from n=0), wrapping around if n exceeds the > * number of present nodes. > */ > static unsigned offset_il_node(struct mempolicy *pol, > struct vm_area_struct *vma, unsigned long n) > { > unsigned nnodes = nodes_weight(pol->v.nodes); > unsigned target; > int i; > int nid; > > if (!nnodes) > return numa_node_id(); > target = (unsigned int)n % nnodes; > nid = first_node(pol->v.nodes); > for (i = 0; i < target; i++) > nid = next_node(nid, pol->v.nodes); > return nid; > } > > > From: Andrew Morton <akpm@linux-foundation.org> > Subject: mm/mempolicy.c:offset_il_node() document and clarify > > This code was pretty obscure and was relying upon obscure side-effects of > next_node(-1, ...) and was relying upon NUMA_NO_NODE being equal to -1. > > Clean that all up and document the function's intent. > > Cc: Vlastimil Babka <vbabka@suse.cz> > Cc: Xishi Qiu <qiuxishi@huawei.com> > Cc: Joonsoo Kim <js1304@gmail.com> > Cc: David Rientjes <rientjes@google.com> > Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > Cc: Laura Abbott <lauraa@codeaurora.org> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
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