On Fri, Nov 01, 2024 at 12:54:38PM -0700, Boqun Feng wrote:
> Paul reported an invalid wait context issue in scftorture catched by
> lockdep, and the cause of the issue is because scf_handler() may call
> kfree() to free the struct scf_check:
>
> static void scf_handler(void *scfc_in)
> {
> [...]
> } else {
> kfree(scfcp);
> }
> }
>
> (call chain anlysis from Marco Elver)
>
> This is problematic because smp_call_function() uses non-threaded
> interrupt and kfree() may acquire a local_lock which is a sleepable lock
> on RT.
>
> The general rule is: do not alloc or free memory in non-threaded
> interrupt conntexts.
>
> A quick fix is to use workqueue to defer the kfree(). However, this is
> OK only because scftorture is test code. In general the users of
> interrupts should avoid giving interrupt handlers the ownership of
> objects, that is, users should handle the lifetime of objects outside
> and interrupt handlers should only hold references to objects.
>
> Reported-by: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/41619255-cdc2-4573-a360-7794fc3614f7@paulmck-laptop/
> Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Thank you!
I was worried that putting each kfree() into a separate workqueue handler
would result in freeing not keeping up with allocation for asynchronous
testing (for example, scftorture.weight_single=1), but it seems to be
doing fine in early testing.
So I have queued this in my -rcu tree for review and further testing.
Thanx, Paul
> ---
> kernel/scftorture.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/scftorture.c b/kernel/scftorture.c
> index 44e83a646264..ab6dcc7c0116 100644
> --- a/kernel/scftorture.c
> +++ b/kernel/scftorture.c
> @@ -127,6 +127,7 @@ static unsigned long scf_sel_totweight;
>
> // Communicate between caller and handler.
> struct scf_check {
> + struct work_struct work;
> bool scfc_in;
> bool scfc_out;
> int scfc_cpu; // -1 for not _single().
> @@ -252,6 +253,13 @@ static struct scf_selector *scf_sel_rand(struct torture_random_state *trsp)
> return &scf_sel_array[0];
> }
>
> +static void kfree_scf_check_work(struct work_struct *w)
> +{
> + struct scf_check *scfcp = container_of(w, struct scf_check, work);
> +
> + kfree(scfcp);
> +}
> +
> // Update statistics and occasionally burn up mass quantities of CPU time,
> // if told to do so via scftorture.longwait. Otherwise, occasionally burn
> // a little bit.
> @@ -296,7 +304,10 @@ static void scf_handler(void *scfc_in)
> if (scfcp->scfc_rpc)
> complete(&scfcp->scfc_completion);
> } else {
> - kfree(scfcp);
> + // Cannot call kfree() directly, pass it to workqueue. It's OK
> + // only because this is test code, avoid this in real world
> + // usage.
> + queue_work(system_wq, &scfcp->work);
> }
> }
>
> @@ -335,6 +346,7 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra
> scfcp->scfc_wait = scfsp->scfs_wait;
> scfcp->scfc_out = false;
> scfcp->scfc_rpc = false;
> + INIT_WORK(&scfcp->work, kfree_scf_check_work);
> }
> }
> switch (scfsp->scfs_prim) {
> --
> 2.45.2
>
