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Chuck Lever
9f3d9b68c1
[ Upstream commite786233d2e] rl_kref formerly served two distinct lifetimes through a single refcount: it gated when a Reply could wake its RPC task, and it gated when an rpcrdma_req could return to its free pool. The marshal path took the Send-side reference only when SGEs needed DMA-unmap (sc_unmap_count > 0), which made a Send carrying only pre-registered buffers an exception: the Reply handler dropped rl_kref from 1 to 0 and freed the req while the HCA might still be DMA-reading from its send buffer. Give rl_kref a narrower job. The RPC layer takes one reference when slot allocation hands a req out. rpcrdma_prepare_send_sges() takes a Send-side reference unconditionally after WR preparation succeeds. xprt_rdma_free_slot() and xprt_rdma_bc_free_rqst() drop the RPC-layer reference; rpcrdma_sendctx_unmap() drops the Send-side reference. The req returns to its free pool only after both owners have signed off. The existing kref_init(&req->rl_kref) call in rpcrdma_prepare_send_sges() is removed. Initialization moves to the slot-allocation paths (xprt_rdma_alloc_slot and rpcrdma_bc_rqst_get), and the release callback re-arms rl_kref before the req returns to a free pool. A re-init in the marshal path would discard the RPC-layer reference that already exists on entry. Three invariants follow: - Any rpcrdma_req held by an rpc_rqst has rl_kref >= 1. xprt_rdma_alloc_slot(), rpcrdma_bc_rqst_get(), and the backlog-wake branch in xprt_rdma_alloc_slot() each kref_init rl_kref before publishing the req. Without this invariant, an RPC task that aborts between slot allocation and marshal (gss_refresh failure or signal during call_connect, for example) would drive xprt_release() -> xprt_rdma_free_slot() -> kref_put against a refcount of zero, saturating refcount_t and stranding the slot. - The Send-side reference is taken only after WR prep succeeds. A mapping failure in rpcrdma_prepare_send_sges() runs rpcrdma_sendctx_cancel(), which DMA-unmaps the sendctx and clears sc_req without touching rl_kref. The sendctx ring walks in rpcrdma_sendctx_put_locked() and rpcrdma_sendctxs_destroy() skip entries with sc_req == NULL, so a burst of -EIO marshal failures cannot hold reqs off rb_send_bufs. - The release callback re-arms rl_kref so the next consumer enters with the invariant satisfied. Replies now complete the RPC directly. rpcrdma_reply_handler() calls rpcrdma_complete_rqst() in place of kref_put on the non-LocalInv branch. The LocalInv branch already completes the RPC from frwr_unmap_async() and is unaffected. Because Send-side references can now outlive RPC completion, connection teardown drains sendctx entries whose unsignaled Sends never had a later signaled completion to walk the ring. rpcrdma_sendctxs_destroy() walks the active range and runs rpcrdma_sendctx_unmap() on each entry with a non-NULL sc_req before the request buffers are reset, and is moved ahead of rpcrdma_reqs_reset() in rpcrdma_xprt_disconnect() so the reqs are still in their pre-reset state when the Send-side refs are released. The drain creates a teardown-ordering hazard on the backchannel path. With the new lifetime, releasing a bc_prealloc req from rpcrdma_req_release() re-adds it to bc_pa_list. The disconnect in xprt_rdma_destroy() runs after xprt_destroy_backchannel() has already emptied bc_pa_list, so the drained reqs would otherwise leak. xprt_rdma_destroy() now runs xprt_rdma_bc_destroy(xprt, 0) a second time after the disconnect to reclaim them. Fixes:0ab1152370("xprtrdma: Wake RPCs directly in rpcrdma_wc_send path") Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <anna.schumaker@hammerspace.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.