5.4-stable review patch. If anyone has any objections, please let me know.
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From: Matthew Wilcox (Oracle) willy@infradead.org
commit f2d5dcb48f7ba9e3ff249d58fc1fa963d374e66a upstream.
ilog2() rounds down, so for example when PowerPC 85xx sets CONFIG_NR_CPUS to 24, we will only allocate 4 bits to store the number of CPUs instead of 5. Use bits_per() instead, which rounds up. Found by code inspection. The effect of this would probably be a misaccounting when doing NUMA balancing, so to a user, it would only be a performance penalty. The effects may be more wide-spread; it's hard to tell.
Link: https://lkml.kernel.org/r/20231010145549.1244748-1-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org Fixes: 90572890d202 ("mm: numa: Change page last {nid,pid} into {cpu,pid}") Reviewed-by: Rik van Riel riel@surriel.com Acked-by: Mel Gorman mgorman@techsingularity.net Cc: Peter Zijlstra peterz@infradead.org Cc: Ingo Molnar mingo@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/bounds.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/bounds.c +++ b/kernel/bounds.c @@ -19,7 +19,7 @@ int main(void) DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS); DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES); #ifdef CONFIG_SMP - DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS)); + DEFINE(NR_CPUS_BITS, bits_per(CONFIG_NR_CPUS)); #endif DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t)); /* End of constants */