A DC_ADD_CAPACITY event can span multiple event records grouped together
by the CXL_DCD_EVENT_MORE flag. Extents are staged in the pending list until
the last event record ('More'=0) is received, at which point the pending
list is processed. If the device opens such a chain (More=1) but never
sends the closing record, the staged list sits indefinitely.Add a delayed-work watchdog that, on expiry, refuses the chain with an empty ADD_DC_RESPONSE and drops the staged list. The 20s timeout is a conservative upper bound and may be tightened later. The timeout is purely defensive — the spec does not require it, but prevents issues from a lost mailbox response or a crashed fabric manager. Signed-off-by: Anisa Su <[email protected]> --- drivers/cxl/core/mbox.c | 73 ++++++++++++++++++++++++++++++++++++++++- drivers/cxl/cxlmem.h | 23 ++++++++++--- 2 files changed, 91 insertions(+), 5 deletions(-) diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c index 1b38f34538f3..c376492fa166 100644 --- a/drivers/cxl/core/mbox.c +++ b/drivers/cxl/core/mbox.c @@ -1219,6 +1219,48 @@ static void clear_pending_extents(void *_mds) mds->add_ctx.group = NULL; } +/* + * Bound on how long the host will wait for a device to finish a + * multi-record DC_ADD_CAPACITY chain (More=1 ... More=0) before + * refusing the chain. + * The timeout is not defined in the spec, but added for defensive purposes. + * Since there is no spec-defined timeout, 20s is chosen as a generous + * upper bound and matches the GPF timeout. + */ +#define CXL_DC_ADD_TIMEOUT (20 * HZ) + +static void cxl_dc_add_timeout(struct work_struct *work) +{ + struct pending_add_ctx *ctx = container_of(to_delayed_work(work), + struct pending_add_ctx, + timeout_work); + struct cxl_memdev_state *mds = container_of(ctx, + struct cxl_memdev_state, + add_ctx); + struct device *dev = mds->cxlds.dev; + + guard(mutex)(&ctx->lock); + + if (!ctx->armed) + return; + + dev_warn(dev, "DC add chain timed out; refusing staged extents\n"); + + if (cxl_send_dc_response(mds, CXL_MBOX_OP_ADD_DC_RESPONSE, + &ctx->pending_extents, 0)) + dev_dbg(dev, "Failed to send empty ADD_DC_RESPONSE on timeout\n"); + + clear_pending_extents(mds); + ctx->armed = false; +} + +static void cxl_cancel_dcd_add_chain_work(void *_mds) +{ + struct cxl_memdev_state *mds = _mds; + + cancel_delayed_work_sync(&mds->add_ctx.timeout_work); +} + static int add_to_pending_list(struct list_head *pending_list, struct cxl_extent *to_add) { @@ -1246,18 +1288,34 @@ static int add_to_pending_list(struct list_head *pending_list, static int handle_add_event(struct cxl_memdev_state *mds, struct cxl_event_dcd *event) { + struct pending_add_ctx *ctx = &mds->add_ctx; struct device *dev = mds->cxlds.dev; int rc; - rc = add_to_pending_list(&mds->add_ctx.pending_extents, &event->extent); + guard(mutex)(&ctx->lock); + + rc = add_to_pending_list(&ctx->pending_extents, &event->extent); if (rc) return rc; if (event->flags & CXL_DCD_EVENT_MORE) { dev_dbg(dev, "more bit set; delay the surfacing of extent\n"); + mod_delayed_work(system_wq, &ctx->timeout_work, + CXL_DC_ADD_TIMEOUT); + ctx->armed = true; return 0; } + /* + * Chain is closing. Disarm before flushing so a pending watchdog + * (queued but blocked on @ctx->lock) sees !armed and bails out. + * cancel_delayed_work() — not _sync — because handle_add_event() + * itself runs on system_wq and a sync cancel of same-wq work can + * deadlock. + */ + ctx->armed = false; + cancel_delayed_work(&ctx->timeout_work); + rc = cxl_send_dc_response(mds, CXL_MBOX_OP_ADD_DC_RESPONSE, &mds->add_ctx.pending_extents, 0); clear_pending_extents(mds); @@ -2009,11 +2067,24 @@ struct cxl_memdev_state *cxl_memdev_state_create(struct device *dev, u64 serial, mutex_init(&mds->event.log_lock); INIT_LIST_HEAD(&mds->add_ctx.pending_extents); + mutex_init(&mds->add_ctx.lock); + INIT_DELAYED_WORK(&mds->add_ctx.timeout_work, + cxl_dc_add_timeout); + mds->add_ctx.armed = false; rc = devm_add_action_or_reset(dev, clear_pending_extents, mds); if (rc) return ERR_PTR(rc); + /* + * Registered after clear_pending_extents so devm's reverse-order + * unwind cancels (and waits for) the watchdog first, then the list + * cleanup runs with the watchdog guaranteed not to refire. + */ + rc = devm_add_action_or_reset(dev, cxl_cancel_dcd_add_chain_work, mds); + if (rc) + return ERR_PTR(rc); + rc = devm_cxl_register_mce_notifier(dev, &mds->mce_notifier); if (rc == -EOPNOTSUPP) dev_warn(dev, "CXL MCE unsupported\n"); diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h index 592c8e3b611c..d992cc9b7811 100644 --- a/drivers/cxl/cxlmem.h +++ b/drivers/cxl/cxlmem.h @@ -8,6 +8,8 @@ #include <linux/uuid.h> #include <linux/node.h> #include <linux/list.h> +#include <linux/mutex.h> +#include <linux/workqueue.h> #include <cxl/event.h> #include <cxl/mailbox.h> #include "cxl.h" @@ -402,19 +404,32 @@ static inline struct cxl_dev_state *mbox_to_cxlds(struct cxl_mailbox *cxl_mbox) /** * struct pending_add_ctx - Staging state for an in-progress - * DCD_ADD_CAPACITY event chain + * DCD_ADD_CAPACITY event chain * @pending_extents: extents received so far in the chain; flushed when - * the chain closes (More=0) + * the chain closes (More=0) * @group: tag group being assembled from the chain + * @timeout_work: watchdog that fires if a chain is opened with + * CXL_DCD_EVENT_MORE but the closing record never arrives + * @lock: serialises updates to the chain state against the watchdog + * @armed: set when a More=1 chain opens; cleared when the chain closes, + * either by a More=0 event record or by the watchdog firing. * * A DCD_ADD_CAPACITY notification can span multiple event records * stitched together by the CXL_DCD_EVENT_MORE flag. Records are staged - * here until the device clears More, at which point the staged batch is - * processed and responded to as a single Add_DC_Response. + * here until an event record with 'More'=0 is received, at which point the + * staged batch is processed and responded to as a single Add_DC_Response. + * + * If a chain is opened (More=1) but the device never sends the closing + * record, the staged list would otherwise sit indefinitely. @timeout_work + * is a defensive watchdog that refuses such a chain with an empty response + * and drops the staged list. */ struct pending_add_ctx { struct list_head pending_extents; struct cxl_dc_tag_group *group; + struct delayed_work timeout_work; + struct mutex lock; + bool armed; }; /** -- 2.43.0
