[Belated Cc linux-m68k...]
On Mon, 25 Aug 2025, Lance Yang 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); 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
Thanks for sending code to illustrate your point. Unfortunately, I was not able to reproduce your results. Tested on x86, your test module shows no misalignment:
[131840.349042] io_lock address offset mod 4: 0
Tested on m68k I also get 0, given the patch at the top of this thread:
[ 0.400000] io_lock address offset mod 4: 0
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.
I don't think so. But there is something unexpected going on here -- the output from pahole appears to say io_lock is at offset 49, which seems to contradict the printk() output above.
struct test_container { char padding[49]; /* 0 49 */ struct mutex io_lock __attribute__((__aligned__(1))); /* 49 12 */
/* size: 61, cachelines: 1, members: 2 */ /* forced alignments: 1 */ /* last cacheline: 61 bytes */ } __attribute__((__packed__));