On Sun, Apr 04, 2021 at 11:24:57AM +0100, Matthew Wilcox wrote: > On Sat, Apr 03, 2021 at 09:15:17PM -0700, syzbot wrote: > > HEAD commit: 2bb25b3a Merge tag 'mips-fixes_5.12_3' of git://git.kernel.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=1284cc31d00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=78ef1d159159890 > > dashboard link: https://syzkaller.appspot.com/bug?extid=dde0cc33951735441301 > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+dde0cc33951735441301@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > WARNING: suspicious RCU usage > > 5.12.0-rc5-syzkaller #0 Not tainted > > ----------------------------- > > kernel/sched/core.c:8294 Illegal context switch in RCU-bh read-side critical section! > > > > other info that might help us debug this: > > > > > > rcu_scheduler_active = 2, debug_locks = 0 > > no locks held by systemd-udevd/4825. > > I think we have something that's taking the RCU read lock in > (soft?) interrupt context and not releasing it properly in all > situations. This thread doesn't have any locks recorded, but > lock_is_held(&rcu_bh_lock_map) is true. > > Is there some debugging code that could find this? eg should > lockdep_softirq_end() check that rcu_bh_lock_map is not held? > (if it's taken in process context, then BHs can't run, so if it's > held at softirq exit, then there's definitely a problem). Hmm, I'm sure i've written something like that at least once, but I can't seem to find it :/ Does something like the completely untested below work for you? --- diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h index 600c10da321a..d8aa1dc481b6 100644 --- a/include/linux/irqflags.h +++ b/include/linux/irqflags.h @@ -54,6 +54,8 @@ extern void trace_hardirqs_off_finish(void); extern void trace_hardirqs_on(void); extern void trace_hardirqs_off(void); +extern void lockdep_validate_context_empty(void); + # define lockdep_hardirq_context() (raw_cpu_read(hardirq_context)) # define lockdep_softirq_context(p) ((p)->softirq_context) # define lockdep_hardirqs_enabled() (this_cpu_read(hardirqs_enabled)) @@ -69,6 +71,7 @@ do { \ } while (0) # define lockdep_hardirq_exit() \ do { \ + lockdep_validate_context_empty(); \ __this_cpu_dec(hardirq_context); \ } while (0) # define lockdep_softirq_enter() \ @@ -77,6 +80,7 @@ do { \ } while (0) # define lockdep_softirq_exit() \ do { \ + lockdep_validate_context_empty(); \ current->softirq_context--; \ } while (0) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 82db977eada8..09ac70d1b3a6 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -2697,6 +2697,37 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev, return 0; } +void lockdep_validate_context_empty(void) +{ + struct task_struct *curr = current; + int depth, ctx = task_irq_context(curr); + + if (debug_locks_silent) + return; + + depth = curr->lockdep_depth; + if (!depth) + return; + + if (curr->held_locks[depth-1].irq_context != ctx) + return; + + + pr_warn("\n"); + pr_warn("====================================\n"); + pr_warn("WARNING: Asymmetric locking detected\n"); + print_kernel_ident(); + pr_warn("------------------------------------\n"); + + pr_warn("%s/%d is leaving an IRQ context with extra locks on\n", + curr->comm, task_pid_nr(curr)); + + lockdep_printk_held_locks(curr); + + printk("\nstack backtrace:\n"); + dump_stack(); +} + #else static inline int check_irq_usage(struct task_struct *curr,
