[PATCH 1/2] kernel/fork: clear PF_BLOCK_TS in copy_process()

[Usama Arif]

PF_BLOCK_TS is only set in blk_time_get_ns() when current->plug is
non-NULL, and blk_finish_plug() clears it via __blk_flush_plug()
before NULLing the plug pointer.  copy_process() breaks the
invariant by inheriting PF_BLOCK_TS from the parent while resetting
the child's plug to NULL.

Clear PF_BLOCK_TS alongside that assignment so callers can rely on
"PF_BLOCK_TS set implies current->plug != NULL" and dereference
current->plug unguarded.

Fixes: 06b23f92af87 ("block: update cached timestamp post schedule/preemption")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Usama Arif <usama.arif@xxxxxxxxx>
---
 kernel/fork.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index 892a95214c54..13e38e89a1f3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2338,6 +2338,7 @@ __latent_entropy struct task_struct *copy_process(
 
 #ifdef CONFIG_BLOCK
 	p->plug = NULL;
+	p->flags &= ~PF_BLOCK_TS;
 #endif
 	futex_init_task(p);
 
-- 
2.53.0-Meta