From: Christophe de Dinechin dinechin@redhat.com
commit 37462a920392cb86541650a6f4121155f11f1199 upstream.
With gcc version 12.0.1 20220401 (Red Hat 12.0.1-0), building with defconfig results in the following compilation error:
| CC mm/swapfile.o | mm/swapfile.c: In function `setup_swap_info': | mm/swapfile.c:2291:47: error: array subscript -1 is below array bounds | of `struct plist_node[]' [-Werror=array-bounds] | 2291 | p->avail_lists[i].prio = 1; | | ~~~~~~~~~~~~~~^~~ | In file included from mm/swapfile.c:16: | ./include/linux/swap.h:292:27: note: while referencing `avail_lists' | 292 | struct plist_node avail_lists[]; /* | | ^~~~~~~~~~~
This is due to the compiler detecting that the mask in node_states[__state] could theoretically be zero, which would lead to first_node() returning -1 through find_first_bit.
I believe that the warning/error is legitimate. I first tried adding a test to check that the node mask is not emtpy, since a similar test exists in the case where MAX_NUMNODES == 1.
However, adding the if statement causes other warnings to appear in for_each_cpu_node_but, because it introduces a dangling else ambiguity. And unfortunately, GCC is not smart enough to detect that the added test makes the case where (node) == -1 impossible, so it still complains with the same message.
This is why I settled on replacing that with a harmless, but relatively useless (node) >= 0 test. Based on the warning for the dangling else, I also decided to fix the case where MAX_NUMNODES == 1 by moving the condition inside the for loop. It will still only be tested once. This ensures that the meaning of an else following for_each_node_mask or derivatives would not silently have a different meaning depending on the configuration.
Link: https://lkml.kernel.org/r/20220414150855.2407137-3-dinechin@redhat.com Signed-off-by: Christophe de Dinechin christophe@dinechin.org Signed-off-by: Christophe de Dinechin dinechin@redhat.com Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: Ben Segall bsegall@google.com Cc: "Michael S. Tsirkin" mst@redhat.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Ingo Molnar mingo@redhat.com Cc: Mel Gorman mgorman@suse.de Cc: Dietmar Eggemann dietmar.eggemann@arm.com Cc: Vincent Guittot vincent.guittot@linaro.org Cc: Paolo Bonzini pbonzini@redhat.com Cc: Daniel Bristot de Oliveira bristot@redhat.com Cc: Jason Wang jasowang@redhat.com Cc: Zhen Lei thunder.leizhen@huawei.com Cc: Juri Lelli juri.lelli@redhat.com Cc: Peter Zijlstra peterz@infradead.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/nodemask.h | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-)
--- a/include/linux/nodemask.h +++ b/include/linux/nodemask.h @@ -365,14 +365,13 @@ static inline void __nodes_fold(nodemask }
#if MAX_NUMNODES > 1 -#define for_each_node_mask(node, mask) \ - for ((node) = first_node(mask); \ - (node) < MAX_NUMNODES; \ - (node) = next_node((node), (mask))) +#define for_each_node_mask(node, mask) \ + for ((node) = first_node(mask); \ + (node >= 0) && (node) < MAX_NUMNODES; \ + (node) = next_node((node), (mask))) #else /* MAX_NUMNODES == 1 */ -#define for_each_node_mask(node, mask) \ - if (!nodes_empty(mask)) \ - for ((node) = 0; (node) < 1; (node)++) +#define for_each_node_mask(node, mask) \ + for ((node) = 0; (node) < 1 && !nodes_empty(mask); (node)++) #endif /* MAX_NUMNODES */
/*