Hi Andrea, Cc+ Petr Pavlu (you can find the whole thread at https://lore.kernel.org/live-patching/[email protected]/T/#t)
On Mon, 12 Oct 2026, Andrea Parri wrote: > Unloading a patched module while a livepatch transition is in progress > can crash the kernel in klp_find_ops(), called from the scheduler. > KCSAN reports > > BUG: KCSAN: data-race in klp_find_ops / klp_unpatch_func > > write (marked) to 0xffff9094c09ece10 of 8 bytes by task 381 on cpu 2: > klp_unpatch_func+0x1bd/0x280 > klp_unpatch_object+0x6a/0x90 > klp_cleanup_module_patches_limited.cold+0x4a/0xd4 > klp_module_going+0x54/0x80 > __do_sys_delete_module+0x247/0x380 > __x64_sys_delete_module+0x39/0x50 > ... > > read to 0xffff9094c09ece10 of 8 bytes by task 146 on cpu 1: > klp_find_ops+0x55/0x90 > klp_check_and_switch_task+0x228/0x320 > klp_try_switch_task+0xb4/0xc0 > __klp_sched_try_switch+0x9a/0xb0 > __schedule+0x60a/0x1450 > schedule+0x3b/0x100 > schedule_timeout+0xc0/0x160 > ra_target_a_loop+0x97/0xa0 [klp_race_target_a] > ... > > followed by > > Oops: general protection fault, probably for non-canonical address > 0xdead000000000110: 0000 [#2] SMP NOPTI > RIP: 0010:klp_find_ops+0x55/0x90 > ... > klp_check_and_switch_task+0x228/0x320 > klp_try_switch_task+0xb4/0xc0 > __klp_sched_try_switch+0x9a/0xb0 > __schedule+0x60a/0x1450 Interesting. So to sum it up... you load a live patch which contains a fix for a module and while the transition is on, you remove the module and it crashes (btw, I do not think that those traces are necessary here. More btw, it would be nice to have a human readable changelog instead of what looks like AI generated description of the patch itself). How did you find the issue? Is it a real problem in production? I wonder whether we could just decline delete_module() in this case and return -EBUSY. It should be a rare operation anyway. Alternatively we could increase refcounts of all patched modules during a transition and decrease them after. Petr P., what do you think? I am not saying we should not do the RCU protection but it feels like a can of worms a bit so if there is an easier way... Regards Miroslav
