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Date: Tue, 14 Jan 2020 17:12:15 +0100 From: Christoph Hellwig <hch@....de> To: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, Waiman Long <longman@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, linux-ext4@...r.kernel.org, cluster-devel@...hat.com Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: [PATCH 02/12] locking/rwsem: Exit early when held by an anonymous owner The rwsem code overloads the owner field with either a task struct or negative magic numbers. Add a quick hack to catch these negative values early on. Without this spinning on a writer that replaced the owner with RWSEM_OWNER_UNKNOWN, rwsem_spin_on_owner can crash while deferencing the task_struct ->on_cpu field of a -8 value. XXX: This might be a bit of a hack as the code otherwise doesn't use the ERR_PTR family macros, better suggestions welcome. Signed-off-by: Christoph Hellwig <hch@....de> --- kernel/locking/rwsem.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 44e68761f432..6adc719a30a1 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -725,6 +725,8 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable) state = rwsem_owner_state(owner, flags, nonspinnable); if (state != OWNER_WRITER) return state; + if (IS_ERR(owner)) + return state; rcu_read_lock(); for (;;) { -- 2.24.1
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