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| author |   Paul E. McKenney <paulmck@kernel.org> | 2020-09-15 14:03:34 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2020-09-16 16:32:38 -0700 |
| commit | 592031cc10858be4adb10f6c0f2608f6f21824aa (patch) | |
| tree | b8c9f82cd7965585fdabc134c5c2c945e7c8050d /kernel/rcu | |
| parent | rcu-tasks: Fix grace-period/unlock race in RCU Tasks Trace (diff) | |
| download | linux-dev-592031cc10858be4adb10f6c0f2608f6f21824aa.tar.xz linux-dev-592031cc10858be4adb10f6c0f2608f6f21824aa.zip | |
rcu-tasks: Fix low-probability task_struct leak
When rcu_tasks_trace_postgp() function detects an RCU Tasks Trace
CPU stall, it adds all tasks blocking the current grace period to
a list, invoking get_task_struct() on each to prevent them from
being freed while on the list. It then traverses that list,
printing stall-warning messages for each one that is still blocking
the current grace period and removing it from the list. The list
removal invokes the matching put_task_struct().
This of course means that in the admittedly unlikely event that some
task executes its outermost rcu_read_unlock_trace() in the meantime, it
won't be removed from the list and put_task_struct() won't be executing,
resulting in a task_struct leak. This commit therefore makes the list
removal and put_task_struct() unconditional, stopping the leak.
Note further that this bug can occur only after an RCU Tasks Trace CPU
stall warning, which by default only happens after a grace period has
extended for ten minutes (yes, not a typo, minutes).
Fixes: 4593e772b502 ("rcu-tasks: Add stall warnings for RCU Tasks Trace")
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: <bpf@vger.kernel.org>
Cc: <stable@vger.kernel.org> # 5.7.x
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tasks.h | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index e583a2d47374..fcd9c25f1140 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -1092,11 +1092,11 @@ static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp) if (READ_ONCE(t->trc_reader_special.b.need_qs)) trc_add_holdout(t, &holdouts); firstreport = true; - list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list) - if (READ_ONCE(t->trc_reader_special.b.need_qs)) { + list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list) { + if (READ_ONCE(t->trc_reader_special.b.need_qs)) show_stalled_task_trace(t, &firstreport); - trc_del_holdout(t); - } + trc_del_holdout(t); // Release task_struct reference. + } if (firstreport) pr_err("INFO: rcu_tasks_trace detected stalls? (Counter/taskslist mismatch?)\n"); show_stalled_ipi_trace(); |