The new adanced API tests want to vet the xarray API is doing what it promises by manually iterating over a set of possible indexes on its own, and using a query operation which holds the RCU lock and then releases it. So it is not using the helper loop options which xarray provides on purpose. Any loop which iterates over 1 million entries (which is possible with order 20, so emulating say a 4 GiB block size) to just to rcu lock and unlock will eventually end up triggering a soft lockup on systems which don't preempt, and have lock provin and RCU prooving enabled. xarray users already use XA_CHECK_SCHED for loops which may take a long time, in our case we don't want to RCU unlock and lock as the caller does that already, but rather just force a schedule every XA_CHECK_SCHED iterations since the test is trying to not trust and rather test that xarray is doing the right thing. [0] https://lkml.kernel.org/r/202402071613.70f28243-lkp@xxxxxxxxx Reported-by: kernel test robot <oliver.sang@xxxxxxxxx> Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> --- lib/test_xarray.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/lib/test_xarray.c b/lib/test_xarray.c index d4e55b4867dc..ac162025cc59 100644 --- a/lib/test_xarray.c +++ b/lib/test_xarray.c @@ -781,6 +781,7 @@ static noinline void *test_get_entry(struct xarray *xa, unsigned long index) { XA_STATE(xas, xa, index); void *p; + static unsigned int i = 0; rcu_read_lock(); repeat: @@ -790,6 +791,17 @@ static noinline void *test_get_entry(struct xarray *xa, unsigned long index) goto repeat; rcu_read_unlock(); + /* + * This is not part of the page cache, this selftest is pretty + * aggressive and does not want to trust the xarray API but rather + * test it, and for order 20 (4 GiB block size) we can loop over + * over a million entries which can cause a soft lockup. Page cache + * APIs won't be stupid, proper page cache APIs loop over the proper + * order so when using a larger order we skip shared entries. + */ + if (++i % XA_CHECK_SCHED == 0) + schedule(); + return p; } -- 2.42.0
