hazptr: handle NULL address in hazptr_detach

When hazptr_acquire loads a NULL pointer, it sets:

- slot_item->slot.addr = NULL,
- slot_item->ctx.ctx = ctx
- ctx->slot = slot

And it returns NULL.

Then hazptr_detach is called on this ctx, it will act on the ctx as if
needed to be promoted to backup slot, even though it has a NULL addr.

Looking at what hazptr_note_context_switch() does before promoting
to backup slot, it checks for a NULL slot->addr, which is exactly
what is missing from hazptr_detach.

With this in place there would be no need to explicitly check the
hazptr_acquire() return value before calling hazptr_detach().

hazptr_release() has a early return check for NULL addr as well, so it
makes sense that detach does an early return (no-op) similarly.

Fixes: 6357ec235c59 ("hazptrtorture: Fix hazptr ownership issue")
Reported-by: kernel test robot <yi1.lai@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202608130915.62b53936-lkp@intel.com
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Bradley Morgan <brads@mainlining.org>
Cc: <rcu@vger.kernel.org>
Cc: <lkmm@lists.linux.dev>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: kernel test robot <yi1.lai@intel.com>

0 files changed, 0 insertions, 0 deletions