[PATCH 0/2] selftests/cgroup: test_zswap: fix single-core flakes

[Wilson Felipe Pereira <wfelipe@google.com>]

When running the cgroup zswap selftests on a single-core VM (-smp 1) with
4GB of RAM, test_zswap_writeback and test_no_kmem_bypass reliably fail on
the initial run after boot due to timing and asynchronous tasks not
completed.

This 2-patch series fixes both initial-run failures:

  * Patch 1 fixes an EBUSY race in test_zswap_writeback() where writing
    "+memory" to cgroup.subtree_control collides with the kernel's
    asynchronous RCU removal of dead child tasks from cgroup.procs.

  * Patch 2 fixes an implicit unsigned integer promotion bug in
    test_no_kmem_bypass() where a small negative delta becomes large when
    compared to an unsigned size_t threshold.

Both tests now reliably pass on the initial run after cold boot on -smp 1
VMs.


Wilson Felipe Pereira (2):
  selftests/cgroup: test_zswap: retry subtree_control write on EBUSY in
    test_zswap_writeback
  selftests/cgroup: test_zswap: fix implicit unsigned promotion bug in
    test_no_kmem_bypass

 tools/testing/selftests/cgroup/test_zswap.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

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2.55.0.571.g244d577d93-goog