From: Ira Weiny Date: Wed, 4 Sep 2024 14:47:54 +0000 (-0500) Subject: cxl/region: Remove lock from memory notifier callback X-Git-Tag: v6.12-rc1~25^2~7 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d9a476c837fab38856c6b6ff9f794c33907a9f81;p=thirdparty%2Flinux.git cxl/region: Remove lock from memory notifier callback In testing Dynamic Capacity Device (DCD) support, a lockdep splat revealed an ABBA issue between the memory notifiers and the DCD extent processing code.[0] Changing the lock ordering within DCD proved difficult because regions must be stable while searching for the proper region and then the device lock must be held to properly notify the DAX region driver of memory changes. Dan points out in the thread that notifiers should be able to trust that it is safe to access static data. Region data is static once the device is realized and until it's destruction. Thus it is better to manage the notifiers within the region driver. Remove the need for a lock by ensuring the notifiers are active only during the region's lifetime. Furthermore, remove cxl_region_nid() because resource can't be NULL while the region is stable. Link: https://lore.kernel.org/all/66b4cf539a79b_a36e829416@iweiny-mobl.notmuch/ [0] Cc: Ying Huang Suggested-by: Dan Williams Reviewed-by: Davidlohr Bueso Reviewed-by: Jonathan Cameron Reviewed-by: Ying Huang Signed-off-by: Ira Weiny Link: https://patch.msgid.link/20240904-fix-notifiers-v3-1-576b4e950266@intel.com Signed-off-by: Dave Jiang --- diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c index 9a7c001eff1e7..7bb79f3f318c4 100644 --- a/drivers/cxl/core/region.c +++ b/drivers/cxl/core/region.c @@ -2313,8 +2313,6 @@ static void unregister_region(void *_cxlr) struct cxl_region_params *p = &cxlr->params; int i; - unregister_memory_notifier(&cxlr->memory_notifier); - unregister_mt_adistance_algorithm(&cxlr->adist_notifier); device_del(&cxlr->dev); /* @@ -2391,18 +2389,6 @@ static bool cxl_region_update_coordinates(struct cxl_region *cxlr, int nid) return true; } -static int cxl_region_nid(struct cxl_region *cxlr) -{ - struct cxl_region_params *p = &cxlr->params; - struct resource *res; - - guard(rwsem_read)(&cxl_region_rwsem); - res = p->res; - if (!res) - return NUMA_NO_NODE; - return phys_to_target_node(res->start); -} - static int cxl_region_perf_attrs_callback(struct notifier_block *nb, unsigned long action, void *arg) { @@ -2415,7 +2401,11 @@ static int cxl_region_perf_attrs_callback(struct notifier_block *nb, if (nid == NUMA_NO_NODE || action != MEM_ONLINE) return NOTIFY_DONE; - region_nid = cxl_region_nid(cxlr); + /* + * No need to hold cxl_region_rwsem; region parameters are stable + * within the cxl_region driver. + */ + region_nid = phys_to_target_node(cxlr->params.res->start); if (nid != region_nid) return NOTIFY_DONE; @@ -2434,7 +2424,11 @@ static int cxl_region_calculate_adistance(struct notifier_block *nb, int *adist = data; int region_nid; - region_nid = cxl_region_nid(cxlr); + /* + * No need to hold cxl_region_rwsem; region parameters are stable + * within the cxl_region driver. + */ + region_nid = phys_to_target_node(cxlr->params.res->start); if (nid != region_nid) return NOTIFY_OK; @@ -2484,14 +2478,6 @@ static struct cxl_region *devm_cxl_add_region(struct cxl_root_decoder *cxlrd, if (rc) goto err; - cxlr->memory_notifier.notifier_call = cxl_region_perf_attrs_callback; - cxlr->memory_notifier.priority = CXL_CALLBACK_PRI; - register_memory_notifier(&cxlr->memory_notifier); - - cxlr->adist_notifier.notifier_call = cxl_region_calculate_adistance; - cxlr->adist_notifier.priority = 100; - register_mt_adistance_algorithm(&cxlr->adist_notifier); - rc = devm_add_action_or_reset(port->uport_dev, unregister_region, cxlr); if (rc) return ERR_PTR(rc); @@ -3387,6 +3373,14 @@ static int is_system_ram(struct resource *res, void *arg) return 1; } +static void shutdown_notifiers(void *_cxlr) +{ + struct cxl_region *cxlr = _cxlr; + + unregister_memory_notifier(&cxlr->memory_notifier); + unregister_mt_adistance_algorithm(&cxlr->adist_notifier); +} + static int cxl_region_probe(struct device *dev) { struct cxl_region *cxlr = to_cxl_region(dev); @@ -3419,6 +3413,18 @@ static int cxl_region_probe(struct device *dev) out: up_read(&cxl_region_rwsem); + if (rc) + return rc; + + cxlr->memory_notifier.notifier_call = cxl_region_perf_attrs_callback; + cxlr->memory_notifier.priority = CXL_CALLBACK_PRI; + register_memory_notifier(&cxlr->memory_notifier); + + cxlr->adist_notifier.notifier_call = cxl_region_calculate_adistance; + cxlr->adist_notifier.priority = 100; + register_mt_adistance_algorithm(&cxlr->adist_notifier); + + rc = devm_add_action_or_reset(&cxlr->dev, shutdown_notifiers, cxlr); if (rc) return rc;