[PATCH] Revert "once: don't use a work queue to reset sleepable static key"

[PATCH] Revert "once: don't use a work queue to reset sleepable static key"

[Eric Dumazet]

This reverts commit e8eef69a99f185e75909adb24ab93d706e07bf27.

While DO_ONCE_SLEEPABLE() is used from sleepable/process context, callers
may still be holding arbitrary subsystem locks.

For instance, __inet_hash_connect() uses get_random_sleepable_once()
which invokes DO_ONCE_SLEEPABLE() while holding the socket lock (sk_lock):

  lock_sock(sk)
    __inet_hash_connect()
      get_random_sleepable_once()
        DO_ONCE_SLEEPABLE()
          __do_once_sleepable_done()
            static_branch_disable()
              static_key_disable()
                cpus_read_lock()

Calling static_branch_disable() directly from __do_once_sleepable_done()
causes static_key_disable() to synchronously acquire cpus_read_lock()
(cpu_hotplug_lock) and jump_label_mutex inside the caller's lock context.

This introduces an unwanted lockdep dependency:
  sk_lock -> cpu_hotplug_lock

Because cpu_hotplug_lock depends on fs_reclaim (via workqueue CPU bringup
allocating memory with GFP_KERNEL), and storage/block layers (such as
NVMe-TCP) acquire sk_lock during I/O dispatch, lockdep reports circular
locking dependencies:

  set->srcu -> sk_lock -> cpu_hotplug_lock -> fs_reclaim -> q_usage_counter -> elevator_lock -> set->srcu

This false positive previously prompted commit 19bdb70c77d3 ("nvme-tcp:
lockdep: use dynamic lockdep keys per socket instance") to work around the
warning using per-socket dynamic keys in NVMe-TCP. That in turn broke
asynchronous socket teardown and caused syzbot warnings in
tcp_tsq_handler().

Restoring once_disable_jump() in __do_once_sleepable_done() ensures that
static_branch_disable() is executed asynchronously from a system workqueue
without holding the caller's locks.

Fixes: e8eef69a99f1 ("once: don't use a work queue to reset sleepable static key")
Cc: stable@vger.kernel.org
Closes: https://lore.kernel.org/lkml/ao0mwtt8ePAINFni@shinhome/
Reported-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Reinette Chatre <reinette.chatre@intel.com>
Cc: Keith Busch <kbusch@kernel.org>
Cc: Nilay Shroff <nilay@linux.ibm.com>
---
 lib/once.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/once.c b/lib/once.c
index d801bfa945e6..0a0a919156e0 100644
--- a/lib/once.c
+++ b/lib/once.c
@@ -93,6 +93,6 @@ void __do_once_sleepable_done(bool *done, struct static_key_true *once_key,
 {
 	*done = true;
 	mutex_unlock(&once_mutex);
-	static_branch_disable(once_key);
+	once_disable_jump(once_key, mod);
 }
 EXPORT_SYMBOL(__do_once_sleepable_done);

base-commit: 66498c75b4f8017f62d720d9b59675bdf3abce91
-- 
2.55.0.860.g4b6b3295ed-goog