On Mon, May 17, 2021 at 06:17:47AM -0700, Tom Rix wrote:

On 5/16/21 7:05 PM, Dennis Zhou wrote:

quoted

Hello,

On Sat, May 15, 2021 at 11:08:17AM -0700, trix@redhat.com wrote:

quoted

From: Tom Rix <trix@redhat.com>

Static analysis reports this problem
percpu.c:2945:6: warning: Assigned value is garbage or undefined
         upa = best_upa;
             ^ ~~~~~~~~
best_upa may not be set, so initialize it.

Signed-off-by: Tom Rix <trix@redhat.com>
---
  mm/percpu.c | 1 +
  1 file changed, 1 insertion(+)

diff --git a/mm/percpu.c b/mm/percpu.c
index a257c3efdf18b..6578b706fae81 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c

@@ -2916,6 +2916,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
  	 * Related to atom_size, which could be much larger than the unit_size.
  	 */
  	last_allocs = INT_MAX;
+	best_upa = max_upa;
  	for (upa = max_upa; upa; upa--) {
  		int allocs = 0, wasted = 0;

-- 
2.26.3

I think the proper fix would be:

best_upa = 0;

I was looking for initializing with something that would work.

I think I prefer setting it to 0 because it forces the loop to have
succeeded vs being able to bypass it if the for loop logic was changed.

quoted

for (...) { }
BUG_ON(!best_upa);

WARN_ON instead?

This is initialization code. So if upa == 0, it really is a problem.
Having 0 units per allocation is bogus.

quoted

upa = best_upa;

If you're fine with this I'll make the changes and apply it to
for-5.13-fixes.

Can you also tell me what static analysis tool produced this? I'm just a
little curious because this code hasn't changed in several years so I'd
have expected some static analyzer to have caught this by now.

Clang 10

Tom

Thanks,
Dennis