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Chuck LeverandGreg Kroah-Hartman
c7a0b17368
[ Upstream commit765bde47fe] xprt_rdma_alloc_slot() and xprt_rdma_free_slot() lack serialization between the buffer pool and the backlog queue. A buffer freed after rpcrdma_buffer_get() finds the pool empty but before rpc_sleep_on() places the task on the backlog is returned to the pool with no waiter to wake, leaving the task stuck on the backlog indefinitely. After joining the backlog, re-check the pool and route any recovered buffer through xprt_wake_up_backlog(), whose queue lock serializes with concurrent wakeups and avoids double-assignment of slots. Because xprt_rdma_free_slot() does not hold reserve_lock, the XPRT_CONGESTED double-check in xprt_throttle_congested() is ineffective: a task can join the backlog through that path after free_slot has already found it empty and cleared the bit. Avoid this by using xprt_add_backlog_noncongested(), which queues the task without setting XPRT_CONGESTED, so every allocation reaches xprt_rdma_alloc_slot() and its post-sleep re-check. Fixes:edb41e61a5("xprtrdma: Make rpc_rqst part of rpcrdma_req") Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com> Stable-dep-of:e786233d2e("xprtrdma: Decouple req recycling from RPC completion") Signed-off-by: Sasha Levin <sashal@kernel.org>