On Mon, 25 Aug 2025 15:46:42 +0800 Lance Yang lance.yang@linux.dev wrote:
On 2025/8/25 14:17, Finn Thain wrote:
On Mon, 25 Aug 2025, Lance Yang wrote:
What if we squash the runtime check fix into your patch?
Did my patch not solve the problem?
Hmm... it should solve the problem for natural alignment, which is a critical fix.
But it cannot solve the problem of forced misalignment from drivers using #pragma pack(1). The runtime warning will still trigger in those cases.
I built a simple test module on a kernel with your patch applied:
#include <linux/module.h> #include <linux/init.h> struct __attribute__((packed)) test_container { char padding[49]; struct mutex io_lock; }; static int __init alignment_init(void) { struct test_container cont; pr_info("io_lock address offset mod 4: %lu\n", (unsigned long)&cont.io_lock % 4);
Doesn't that give a compilation warning from 'taking the address of a packed member'? Ignore that at your peril.
More problematic is that, IIRC, m68k kmalloc() allocates 16bit aligned memory. This has broken other things in the past. I doubt that increasing the alignment to 32bits would make much difference to the kernel memory footprint.
David
return 0;}
static void __exit alignment_exit(void) { pr_info("Module unloaded\n"); }
module_init(alignment_init); module_exit(alignment_exit); MODULE_LICENSE("GPL"); MODULE_AUTHOR("x"); MODULE_DESCRIPTION("x");
Result from dmesg: [Mon Aug 25 15:44:50 2025] io_lock address offset mod 4: 1 As we can see, a packed struct can still force the entire mutex object to an unaligned address. With an address like this, the WARN_ON_ONCE can still be triggered. That's why I proposed squashing the runtime check fix into your patch. Then it can be cleanly backported to stop all the spurious warnings at once. I hope this clarifies things.