On Fri, 14 Jun 2019, Steven Rostedt wrote: > On Thu, 13 Jun 2019 20:07:22 -0500 > Josh Poimboeuf <jpoim...@redhat.com> wrote: > > > It's possible for livepatch and ftrace to be toggling a module's text > > permissions at the same time, resulting in the following panic: > > > > [..] > > > The above panic occurs when loading two modules at the same time with > > ftrace enabled, where at least one of the modules is a livepatch module: > > > > CPU0 CPU1 > > klp_enable_patch() > > klp_init_object_loaded() > > module_disable_ro() > > ftrace_module_enable() > > ftrace_arch_code_modify_post_process() > > set_all_modules_text_ro() > > klp_write_object_relocations() > > apply_relocate_add() > > *patches read-only code* - BOOM > > > > A similar race exists when toggling ftrace while loading a livepatch > > module. > > > > Fix it by ensuring that the livepatch and ftrace code patching > > operations -- and their respective permissions changes -- are protected > > by the text_mutex. > > > > Reported-by: Johannes Erdfelt <johan...@erdfelt.com> > > Fixes: 444d13ff10fb ("modules: add ro_after_init support") > > Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com> > > Acked-by: Jessica Yu <j...@kernel.org> > > Reviewed-by: Petr Mladek <pmla...@suse.com> > > Reviewed-by: Miroslav Benes <mbe...@suse.cz> > > This patch looks uncontroversial. I'm going to pull this one in and > start testing it. And if it works, I'll push to Linus.
Triggered this on s390x. Masami CCed and Linus as well, because the patch is in master branch and we are after -rc6. Thomas CCed because of commit 2d1e38f56622 ("kprobes: Cure hotplug lock ordering issues"). ====================================================== WARNING: possible circular locking dependency detected 5.2.0-rc6 #1 Tainted: G O K ------------------------------------------------------ insmod/1393 is trying to acquire lock: 000000002fdee887 (cpu_hotplug_lock.rw_sem){++++}, at: stop_machine+0x2e/0x60 but task is already holding lock: 000000005b22fb82 (text_mutex){+.+.}, at: ftrace_run_update_code+0x2a/0xa0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (text_mutex){+.+.}: validate_chain.isra.21+0xb32/0xd70 __lock_acquire+0x4b8/0x928 lock_acquire+0x102/0x230 __mutex_lock+0x88/0x908 mutex_lock_nested+0x32/0x40 register_kprobe+0x254/0x658 init_kprobes+0x11a/0x168 do_one_initcall+0x70/0x318 kernel_init_freeable+0x456/0x508 kernel_init+0x22/0x150 ret_from_fork+0x30/0x34 kernel_thread_starter+0x0/0xc -> #0 (cpu_hotplug_lock.rw_sem){++++}: check_prev_add+0x90c/0xde0 validate_chain.isra.21+0xb32/0xd70 __lock_acquire+0x4b8/0x928 lock_acquire+0x102/0x230 cpus_read_lock+0x62/0xd0 stop_machine+0x2e/0x60 arch_ftrace_update_code+0x2e/0x40 ftrace_run_update_code+0x40/0xa0 ftrace_startup+0xb2/0x168 register_ftrace_function+0x64/0x88 klp_patch_object+0x1a2/0x290 klp_enable_patch+0x554/0x980 do_one_initcall+0x70/0x318 do_init_module+0x6e/0x250 load_module+0x1782/0x1990 __s390x_sys_finit_module+0xaa/0xf0 system_call+0xd8/0x2d0 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(text_mutex); lock(cpu_hotplug_lock.rw_sem); lock(text_mutex); lock(cpu_hotplug_lock.rw_sem); *** DEADLOCK *** 3 locks held by insmod/1393: #0: 00000000a9723159 (klp_mutex){+.+.}, at: klp_enable_patch+0x62/0x980 #1: 00000000bd173ffc (ftrace_lock){+.+.}, at: register_ftrace_function+0x56/0x88 #2: 000000005b22fb82 (text_mutex){+.+.}, at: ftrace_run_update_code+0x2a/0xa0 stack backtrace: CPU: 0 PID: 1393 Comm: insmod Tainted: G O K 5.2.0-rc6 #1 Hardware name: IBM 2827 H43 400 (KVM/Linux) Call Trace: ([<00000000682100b4>] show_stack+0xb4/0x130) [<0000000068adeb8c>] dump_stack+0x94/0xd8 [<00000000682b563c>] print_circular_bug+0x1f4/0x328 [<00000000682b7264>] check_prev_add+0x90c/0xde0 [<00000000682b826a>] validate_chain.isra.21+0xb32/0xd70 [<00000000682ba018>] __lock_acquire+0x4b8/0x928 [<00000000682ba952>] lock_acquire+0x102/0x230 [<0000000068243c12>] cpus_read_lock+0x62/0xd0 [<0000000068336bf6>] stop_machine+0x2e/0x60 [<0000000068355b3e>] arch_ftrace_update_code+0x2e/0x40 [<0000000068355b90>] ftrace_run_update_code+0x40/0xa0 [<000000006835971a>] ftrace_startup+0xb2/0x168 [<0000000068359834>] register_ftrace_function+0x64/0x88 [<00000000682e8a9a>] klp_patch_object+0x1a2/0x290 [<00000000682e7d64>] klp_enable_patch+0x554/0x980 [<00000000681fcaa0>] do_one_initcall+0x70/0x318 [<000000006831449e>] do_init_module+0x6e/0x250 [<0000000068312b52>] load_module+0x1782/0x1990 [<0000000068313002>] __s390x_sys_finit_module+0xaa/0xf0 [<0000000068b03f30>] system_call+0xd8/0x2d0 INFO: lockdep is turned off. If I am reading the code correctly, ftrace_run_update_code() takes text_mutex now and then calls stop_machine(), which grabs cpu_hotplug_lock for reading. do_optimize_kprobes() (see the comment there) expects cpu_hotplug_lock to be held and takes text_mutex. Whoops. Maybe there is a simple fix, but reverting the commit in this stage seems warranted. Miroslav