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count","web_links":[{"name":"gitweb","tooltip":"Open in GitWeb","url":"/gitweb?p\u003duserspace-rcu.git;a\u003dcommit;h\u003d59b6b14faa1ef105997fdffd9048ec56b3808ce8"}]}],"author":{"name":"Mathieu Desnoyers","email":"mathieu.desnoyers@efficios.com","date":"2022-06-22 20:28:53.000000000","tz":-240},"committer":{"name":"Mathieu Desnoyers","email":"mathieu.desnoyers@efficios.com","date":"2022-06-22 20:28:53.000000000","tz":-240},"subject":"Fix: workqueue: futex wait: handle spurious futex wakeups","message":"Fix: workqueue: futex wait: handle spurious futex wakeups\n\nFrom futex(5):\n\n       FUTEX_WAIT\n              Returns 0 if the caller was woken up.  Note that a  wake-up  can\n              also  be caused by common futex usage patterns in unrelated code\n              that happened to have previously used the  futex  word\u0027s  memory\n              location  (e.g., typical futex-based implementations of Pthreads\n              mutexes can cause this under some conditions).  Therefore, call‐\n              ers should always conservatively assume that a return value of 0\n              can mean a spurious wake-up, and  use  the  futex  word\u0027s  value\n              (i.e.,  the user-space synchronization scheme) to decide whether\n              to continue to block or not.\n\nWe therefore need to validate whether the value differs from -1 in\nuser-space after the call to FUTEX_WAIT returns 0.\n\nSigned-off-by: Mathieu Desnoyers \u003cmathieu.desnoyers@efficios.com\u003e\nChange-Id: Id024e7d3b2dab75d30fc01280fd27e5f2d8af0d1\n","web_links":[{"name":"gitweb","tooltip":"Open in GitWeb","url":"/gitweb?p\u003duserspace-rcu.git;a\u003dcommit;h\u003d08bb27c338b24b19d850c6ec4841258a32601d05"}],"resolve_conflicts_web_links":[{"name":"gitweb","tooltip":"Open in GitWeb","url":"/gitweb?p\u003duserspace-rcu.git;a\u003dcommit;h\u003d08bb27c338b24b19d850c6ec4841258a32601d05"}]},"branch":"refs/heads/master"},"34c0b948417e9f85b6e62560ce8f372b1a0672c1":{"kind":"NO_CODE_CHANGE","_number":2,"created":"2022-06-23 19:09:31.000000000","uploader":{"_account_id":1000009,"name":"Mathieu Desnoyers","email":"mathieu.desnoyers@efficios.com","username":"compudj","avatars":[{"url":"https://www.gravatar.com/avatar/7326b3e1d32b971a5e69d9730228c428.jpg?d\u003dretro\u0026r\u003dr\u0026s\u003d32","height":32},{"url":"https://www.gravatar.com/avatar/7326b3e1d32b971a5e69d9730228c428.jpg?d\u003dretro\u0026r\u003dr\u0026s\u003d56","height":56},{"url":"https://www.gravatar.com/avatar/7326b3e1d32b971a5e69d9730228c428.jpg?d\u003dretro\u0026r\u003dr\u0026s\u003d100","height":100},{"url":"https://www.gravatar.com/avatar/7326b3e1d32b971a5e69d9730228c428.jpg?d\u003dretro\u0026r\u003dr\u0026s\u003d120","height":120}]},"ref":"refs/changes/41/8441/2","fetch":{"anonymous http":{"url":"https://review.lttng.org/userspace-rcu","ref":"refs/changes/41/8441/2","commands":{"Branch":"git fetch https://review.lttng.org/userspace-rcu refs/changes/41/8441/2 \u0026\u0026 git checkout -b change-8441 FETCH_HEAD","Checkout":"git fetch https://review.lttng.org/userspace-rcu refs/changes/41/8441/2 \u0026\u0026 git checkout FETCH_HEAD","Cherry Pick":"git fetch https://review.lttng.org/userspace-rcu refs/changes/41/8441/2 \u0026\u0026 git cherry-pick FETCH_HEAD","Format Patch":"git fetch https://review.lttng.org/userspace-rcu refs/changes/41/8441/2 \u0026\u0026 git format-patch -1 --stdout FETCH_HEAD","Pull":"git pull https://review.lttng.org/userspace-rcu refs/changes/41/8441/2","Reset To":"git fetch https://review.lttng.org/userspace-rcu refs/changes/41/8441/2 \u0026\u0026 git reset --hard FETCH_HEAD"}}},"commit":{"parents":[{"commit":"59b6b14faa1ef105997fdffd9048ec56b3808ce8","subject":"Fix: Use %lu rather than %ld to print count","web_links":[{"name":"gitweb","tooltip":"Open in GitWeb","url":"/gitweb?p\u003duserspace-rcu.git;a\u003dcommit;h\u003d59b6b14faa1ef105997fdffd9048ec56b3808ce8"}]}],"author":{"name":"Mathieu Desnoyers","email":"mathieu.desnoyers@efficios.com","date":"2022-06-22 20:28:53.000000000","tz":-240},"committer":{"name":"Mathieu Desnoyers","email":"mathieu.desnoyers@efficios.com","date":"2022-06-23 19:09:18.000000000","tz":-240},"subject":"Fix: workqueue: futex wait: handle spurious futex wakeups","message":"Fix: workqueue: futex wait: handle spurious futex wakeups\n\nObserved issue\n\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\n\nThe workqueue thread futex_wait() returns with a workqueue-\u003efutex state\nof -1, which is unexpected. In this situation, the workqueue thread is\nobserved to use 99% of CPU as workqueue-\u003efutex values are decremented to\nvery low negative values while the workqueue is empty.\n\nThis issue will cause spurious unexpected high CPU use, but will not\nlead to data corruption.\n\nCause\n\u003d\u003d\u003d\u003d\u003d\n\nFrom futex(5):\n\n       FUTEX_WAIT\n              Returns 0 if the caller was woken up.  Note that a  wake-up  can\n              also  be caused by common futex usage patterns in unrelated code\n              that happened to have previously used the  futex  word\u0027s  memory\n              location  (e.g., typical futex-based implementations of Pthreads\n              mutexes can cause this under some conditions).  Therefore, call‐\n              ers should always conservatively assume that a return value of 0\n              can mean a spurious wake-up, and  use  the  futex  word\u0027s  value\n              (i.e.,  the user-space synchronization scheme) to decide whether\n              to continue to block or not.\n\nSolution\n\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\n\nWe therefore need to validate whether the value differs from -1 in\nuser-space after the call to FUTEX_WAIT returns 0.\n\nKnown drawbacks\n\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\n\nNone.\n\nSigned-off-by: Mathieu Desnoyers \u003cmathieu.desnoyers@efficios.com\u003e\nChange-Id: Id024e7d3b2dab75d30fc01280fd27e5f2d8af0d1\n","web_links":[{"name":"gitweb","tooltip":"Open in GitWeb","url":"/gitweb?p\u003duserspace-rcu.git;a\u003dcommit;h\u003d34c0b948417e9f85b6e62560ce8f372b1a0672c1"}],"resolve_conflicts_web_links":[{"name":"gitweb","tooltip":"Open in GitWeb","url":"/gitweb?p\u003duserspace-rcu.git;a\u003dcommit;h\u003d34c0b948417e9f85b6e62560ce8f372b1a0672c1"}]},"branch":"refs/heads/master"},"80c34c2de3d970eb82049798357743cfa71e8b54":{"kind":"NO_CHANGE","_number":3,"created":"2022-06-27 14:30:14.000000000","uploader":{"_account_id":1000009,"name":"Mathieu Desnoyers","email":"mathieu.desnoyers@efficios.com","username":"compudj","avatars":[{"url":"https://www.gravatar.com/avatar/7326b3e1d32b971a5e69d9730228c428.jpg?d\u003dretro\u0026r\u003dr\u0026s\u003d32","height":32},{"url":"https://www.gravatar.com/avatar/7326b3e1d32b971a5e69d9730228c428.jpg?d\u003dretro\u0026r\u003dr\u0026s\u003d56","height":56},{"url":"https://www.gravatar.com/avatar/7326b3e1d32b971a5e69d9730228c428.jpg?d\u003dretro\u0026r\u003dr\u0026s\u003d100","height":100},{"url":"https://www.gravatar.com/avatar/7326b3e1d32b971a5e69d9730228c428.jpg?d\u003dretro\u0026r\u003dr\u0026s\u003d120","height":120}]},"ref":"refs/changes/41/8441/3","fetch":{"anonymous http":{"url":"https://review.lttng.org/userspace-rcu","ref":"refs/changes/41/8441/3","commands":{"Branch":"git fetch https://review.lttng.org/userspace-rcu refs/changes/41/8441/3 \u0026\u0026 git checkout -b change-8441 FETCH_HEAD","Checkout":"git fetch https://review.lttng.org/userspace-rcu refs/changes/41/8441/3 \u0026\u0026 git checkout FETCH_HEAD","Cherry Pick":"git fetch https://review.lttng.org/userspace-rcu refs/changes/41/8441/3 \u0026\u0026 git cherry-pick FETCH_HEAD","Format Patch":"git fetch https://review.lttng.org/userspace-rcu refs/changes/41/8441/3 \u0026\u0026 git format-patch -1 --stdout FETCH_HEAD","Pull":"git pull https://review.lttng.org/userspace-rcu refs/changes/41/8441/3","Reset To":"git fetch https://review.lttng.org/userspace-rcu refs/changes/41/8441/3 \u0026\u0026 git reset --hard FETCH_HEAD"}}},"commit":{"parents":[{"commit":"59b6b14faa1ef105997fdffd9048ec56b3808ce8","subject":"Fix: Use %lu rather than %ld to print count","web_links":[{"name":"gitweb","tooltip":"Open in GitWeb","url":"/gitweb?p\u003duserspace-rcu.git;a\u003dcommit;h\u003d59b6b14faa1ef105997fdffd9048ec56b3808ce8"}]}],"author":{"name":"Mathieu Desnoyers","email":"mathieu.desnoyers@efficios.com","date":"2022-06-22 20:28:53.000000000","tz":-240},"committer":{"name":"Mathieu Desnoyers","email":"mathieu.desnoyers@efficios.com","date":"2022-06-27 14:30:13.000000000","tz":-240},"subject":"Fix: workqueue: futex wait: handle spurious futex wakeups","message":"Fix: workqueue: futex wait: handle spurious futex wakeups\n\nObserved issue\n\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\n\nThe workqueue thread futex_wait() returns with a workqueue-\u003efutex state\nof -1, which is unexpected. In this situation, the workqueue thread is\nobserved to use 99% of CPU as workqueue-\u003efutex values are decremented to\nvery low negative values while the workqueue is empty.\n\nThis issue will cause spurious unexpected high CPU use, but will not\nlead to data corruption.\n\nCause\n\u003d\u003d\u003d\u003d\u003d\n\nFrom futex(5):\n\n       FUTEX_WAIT\n              Returns 0 if the caller was woken up.  Note that a  wake-up  can\n              also  be caused by common futex usage patterns in unrelated code\n              that happened to have previously used the  futex  word\u0027s  memory\n              location  (e.g., typical futex-based implementations of Pthreads\n              mutexes can cause this under some conditions).  Therefore, call‐\n              ers should always conservatively assume that a return value of 0\n              can mean a spurious wake-up, and  use  the  futex  word\u0027s  value\n              (i.e.,  the user-space synchronization scheme) to decide whether\n              to continue to block or not.\n\nSolution\n\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\n\nWe therefore need to validate whether the value differs from -1 in\nuser-space after the call to FUTEX_WAIT returns 0.\n\nKnown drawbacks\n\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\u003d\n\nNone.\n\nSigned-off-by: Mathieu Desnoyers \u003cmathieu.desnoyers@efficios.com\u003e\nChange-Id: Id024e7d3b2dab75d30fc01280fd27e5f2d8af0d1\n","web_links":[{"name":"gitweb","tooltip":"Open in GitWeb","url":"/gitweb?p\u003duserspace-rcu.git;a\u003dcommit;h\u003d80c34c2de3d970eb82049798357743cfa71e8b54"}],"resolve_conflicts_web_links":[{"name":"gitweb","tooltip":"Open in GitWeb","url":"/gitweb?p\u003duserspace-rcu.git;a\u003dcommit;h\u003d80c34c2de3d970eb82049798357743cfa71e8b54"}]},"branch":"refs/heads/master"}},"requirements":[],"submit_records":[],"submit_requirements":[]}