Messages in this thread Patch in this message | | | From | Tetsuo Handa <> | Subject | [PATCH 1/2] lockdep: Use for_each_process_thread() for debug_show_all_locks() | Date | Fri, 6 Apr 2018 19:41:18 +0900 |
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debug_show_all_locks() tries to grab tasklist_lock for two seconds, but calling while_each_thread() without tasklist_lock held is not safe. See commit 4449a51a7c281602 ("vm_is_stack: use for_each_thread() rather then buggy while_each_thread()") for more information.
Change debug_show_all_locks() from "do_each_thread()/while_each_thread() with possibility of missing tasklist_lock" to "for_each_process_thread() with RCU", and add a call to touch_all_softlockup_watchdogs() like show_state_filter() does.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> --- kernel/locking/lockdep.c | 43 ++++++++----------------------------------- 1 file changed, 8 insertions(+), 35 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 0233863..94f4d21 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -4451,8 +4451,6 @@ void debug_check_no_locks_held(void) void debug_show_all_locks(void) { struct task_struct *g, *p; - int count = 10; - int unlock = 1; if (unlikely(!debug_locks)) { pr_warn("INFO: lockdep is turned off.\n"); @@ -4460,30 +4458,8 @@ void debug_show_all_locks(void) } pr_warn("\nShowing all locks held in the system:\n"); - /* - * Here we try to get the tasklist_lock as hard as possible, - * if not successful after 2 seconds we ignore it (but keep - * trying). This is to enable a debug printout even if a - * tasklist_lock-holding task deadlocks or crashes. - */ -retry: - if (!read_trylock(&tasklist_lock)) { - if (count == 10) - pr_warn("hm, tasklist_lock locked, retrying... "); - if (count) { - count--; - pr_cont(" #%d", 10-count); - mdelay(200); - goto retry; - } - pr_cont(" ignoring it.\n"); - unlock = 0; - } else { - if (count != 10) - pr_cont(" locked it.\n"); - } - - do_each_thread(g, p) { + rcu_read_lock(); + for_each_process_thread(g, p) { /* * It's not reliable to print a task's held locks * if it's not sleeping (or if it's not the current @@ -4491,19 +4467,16 @@ void debug_show_all_locks(void) */ if (p->state == TASK_RUNNING && p != current) continue; - if (p->lockdep_depth) - lockdep_print_held_locks(p); - if (!unlock) - if (read_trylock(&tasklist_lock)) - unlock = 1; + if (!p->lockdep_depth) + continue; + lockdep_print_held_locks(p); touch_nmi_watchdog(); - } while_each_thread(g, p); + touch_all_softlockup_watchdogs(); + } + rcu_read_unlock(); pr_warn("\n"); pr_warn("=============================================\n\n"); - - if (unlock) - read_unlock(&tasklist_lock); } EXPORT_SYMBOL_GPL(debug_show_all_locks); #endif -- 1.8.3.1
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