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Mon, 03 Aug 2026 21:21:15 -0700 (PDT) Date: Tue, 4 Aug 2026 04:20:43 +0000 Mime-Version: 1.0 X-Mailer: git-send-email 2.55.0.571.g244d577d93-goog Message-ID: <20260804042053.56940-1-wfelipe@google.com> Subject: [PATCH 0/2] selftests/cgroup: test_zswap: fix single-core flakes From: Wilson Felipe Pereira To: Johannes Weiner , Yosry Ahmed , Nhat Pham , Chengming Zhou , Tejun Heo , "=?UTF-8?q?Michal=20Koutn=C3=BD?=" , Shuah Khan Cc: linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kselftest@vger.kernel.org, Wilson Felipe Pereira Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: axgyaitekn4d5ignjt6i5x5qjgc96b7u X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 8D66940009 X-HE-Tag: 1785817276-175911 X-HE-Meta: U2FsdGVkX1+qha7381kl1bq2Yq2t2+v2opE+Z1j1oVua66rgafh2Qz2yC+lQDP79wh9AEQSk7Rj45GO+W2Vz5b8+CNhJPMG+Xd2oO1huvuUEnElNrUXeBgCoWMHJEEwEacpx+o+39YKTqM/hTlwOXWVM6/Lj9WIsEmUMi9GruNg7vATY06VAE2P6mrTqnm1cTXfVUXM4vTqfF/nDXwYyAE5Oh7OFGOW2RrV6ssSNOEHfGuBTGxcvgs7BhX2OGa1B+0JuDx+NKaeCZyLil3fhaRLVPY6bJ8TR8dRbNT70qwIM1lVjZRbf+yB0P7bcvBIBtrE7pfWW7s9s6yJn7td+HaiehEfRSjctt7JiPTfrhTW6NAZ5+0wTgS+AVOze1y35LiRpF8ffgbf8GdTAhHKuQZRjlGCRad2d1twURaJxznnPpA6yVmhhiCJwDfDutQgactqjqXZLIhbFjnJ0zLPkWW3hfB5tYCj31PGca3rMifuhZiuta4h0iiCSPanFEWm4RDbsx3yr9c/N/iLt4CDmlOiOPyAzIzlZaVh1VADJEOOuTEQjCTXiuBOxZJKPFBRBoGFFjDTer1hoS2jlobVaVUEeu1W8OooGLSWaCDFr+v868hL0hC8+TtcabzoZDgpbXCEcKQvmUI7PrQ4O2l9wBdsjgVUX0UzybkoirAHV2Z1vqt4JycilqrNavx/HVapkhtVvRR6ohZ6Dy8YXMgqeWTmoZxh3WNp23zy9dgslViFA8/i7vBcqD0w6JocLSvjaGkC03wGDdxN/R6PlNleC0aOuznplItBn6zDYxpr6C0bMr3WH4tknTayyr7xc9+M5oqlRAQhpVpzDgS6eueuwWRGHKrpUETkFdzeIlkKadrZan4jgU+pt4aCNVt5ZaIVVFOTkLdAN+W9jIEExgGPJ8FRac98NsJMQj/Ol89n4TQgFxRIbkJmAwuljm/NHKJ2gabFJYfVVrP3kRD2noBy MHP6e/jD 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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(-) -- 2.55.0.571.g244d577d93-goog