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 <[email protected]>
Closes: https://lore.kernel.org/oe-lkp/[email protected]
Signed-off-by: Mathieu Desnoyers <[email protected]>
Reviewed-by: Bradley Morgan <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Bradley Morgan <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
---
include/linux/hazptr.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/include/linux/hazptr.h b/include/linux/hazptr.h
index 43122c5673bd..d1670121947a 100644
--- a/include/linux/hazptr.h
+++ b/include/linux/hazptr.h
@@ -160,10 +160,12 @@ void hazptr_detach(struct hazptr_ctx *ctx)
struct hazptr_slot *slot;
guard(preempt)();
+ slot = ctx->slot;
+ if (!slot->addr)
+ return;
#ifdef CONFIG_HAZPTR_DEBUG
ctx->detach_task = ctx->detach_cpu = true;
#endif
- slot = ctx->slot;
if (unlikely(hazptr_slot_is_backup(ctx, slot)))
return;
hazptr_promote_to_backup_slot(ctx, slot);
--
2.43.0
