Commit 7b6216ba authored by Saket Kumar Bhaskar's avatar Saket Kumar Bhaskar Committed by Tejun Heo
Browse files

sched_ext: Fix scx_enable() crash on helper kthread creation failure 



A crash was observed when the sched_ext selftests runner was
terminated with Ctrl+\ while test 15 was running:

NIP [c00000000028fa58] scx_enable.constprop.0+0x358/0x12b0
LR [c00000000028fa2c] scx_enable.constprop.0+0x32c/0x12b0
Call Trace:
scx_enable.constprop.0+0x32c/0x12b0 (unreliable)
bpf_struct_ops_link_create+0x18c/0x22c
__sys_bpf+0x23f8/0x3044
sys_bpf+0x2c/0x6c
system_call_exception+0x124/0x320
system_call_vectored_common+0x15c/0x2ec

kthread_run_worker() returns an ERR_PTR() on failure rather than NULL,
but the current code in scx_alloc_and_add_sched() only checks for a NULL
helper. Incase of failure on SIGQUIT, the error is not handled in
scx_alloc_and_add_sched() and scx_enable() ends up dereferencing an
error pointer.

Error handling is fixed in scx_alloc_and_add_sched() to propagate
PTR_ERR() into ret, so that scx_enable() jumps to the existing error
path, avoiding random dereference on failure.

Fixes: bff3b5ae ("sched_ext: Move disable machinery into scx_sched")
Cc: stable@vger.kernel.org # v6.16+
Reported-and-tested-by: default avatarSamir Mulani <samir@linux.ibm.com>
Signed-off-by: default avatarSaket Kumar Bhaskar <skb99@linux.ibm.com>
Reviewed-by: default avatarEmil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: default avatarAndrea Righi <arighi@nvidia.com>
Reviewed-by: default avatarVishal Chourasia <vishalc@linux.ibm.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 36c6f3c0

kernel/sched/ext.c

+4 −1
Original line number Diff line number Diff line
@@ -4479,8 +4479,11 @@ static struct scx_sched *scx_alloc_and_add_sched(struct sched_ext_ops *ops) 
		goto err_free_gdsqs;



	sch->helper = kthread_run_worker(0, "sched_ext_helper");

	if (!sch->helper)

	if (IS_ERR(sch->helper)) {

		ret = PTR_ERR(sch->helper);

		goto err_free_pcpu;

	}



	sched_set_fifo(sch->helper->task);



	atomic_set(&sch->exit_kind, SCX_EXIT_NONE);