From 86c8ea0f3b32aae6d824bdc0d835b6a9361dc912 Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Mon, 31 Jan 2022 15:35:18 -0800 Subject: cxl/core/port: Use dedicated lock for decoder target list Lockdep reports: ====================================================== WARNING: possible circular locking dependency detected 5.16.0-rc1+ #142 Tainted: G OE ------------------------------------------------------ cxl/1220 is trying to acquire lock: ffff979b85475460 (kn->active#144){++++}-{0:0}, at: __kernfs_remove+0x1ab/0x1e0 but task is already holding lock: ffff979b87ab38e8 (&dev->lockdep_mutex#2/4){+.+.}-{3:3}, at: cxl_remove_ep+0x50c/0x5c0 [cxl_core] ...where cxl_remove_ep() is a helper that wants to delete ports while holding a lock on the host device for that port. That sets up a lockdep violation whereby target_list_show() can not rely holding the decoder's device lock while walking the target_list. Switch to a dedicated seqlock for this purpose. Reported-by: Ben Widawsky Reviewed-by: Jonathan Cameron Link: https://lore.kernel.org/r/164367209095.208169.1171673319121271280.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Dan Williams --- drivers/cxl/core/port.c | 30 +++++++++++++++++++++++------- drivers/cxl/cxl.h | 2 ++ 2 files changed, 25 insertions(+), 7 deletions(-) (limited to 'drivers/cxl') diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c index 9285cdb734b2..fc5d86222bc3 100644 --- a/drivers/cxl/core/port.c +++ b/drivers/cxl/core/port.c @@ -104,14 +104,11 @@ static ssize_t target_type_show(struct device *dev, } static DEVICE_ATTR_RO(target_type); -static ssize_t target_list_show(struct device *dev, - struct device_attribute *attr, char *buf) +static ssize_t emit_target_list(struct cxl_decoder *cxld, char *buf) { - struct cxl_decoder *cxld = to_cxl_decoder(dev); ssize_t offset = 0; int i, rc = 0; - cxl_device_lock(dev); for (i = 0; i < cxld->interleave_ways; i++) { struct cxl_dport *dport = cxld->target[i]; struct cxl_dport *next = NULL; @@ -124,13 +121,29 @@ static ssize_t target_list_show(struct device *dev, rc = sysfs_emit_at(buf, offset, "%d%s", dport->port_id, next ? "," : ""); if (rc < 0) - break; + return rc; offset += rc; } - cxl_device_unlock(dev); + + return offset; +} + +static ssize_t target_list_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + struct cxl_decoder *cxld = to_cxl_decoder(dev); + ssize_t offset; + unsigned int seq; + int rc; + + do { + seq = read_seqbegin(&cxld->target_lock); + rc = emit_target_list(cxld, buf); + } while (read_seqretry(&cxld->target_lock, seq)); if (rc < 0) return rc; + offset = rc; rc = sysfs_emit_at(buf, offset, "\n"); if (rc < 0) @@ -494,15 +507,17 @@ static int decoder_populate_targets(struct cxl_decoder *cxld, goto out_unlock; } + write_seqlock(&cxld->target_lock); for (i = 0; i < cxld->nr_targets; i++) { struct cxl_dport *dport = find_dport(port, target_map[i]); if (!dport) { rc = -ENXIO; - goto out_unlock; + break; } cxld->target[i] = dport; } + write_sequnlock(&cxld->target_lock); out_unlock: cxl_device_unlock(&port->dev); @@ -543,6 +558,7 @@ static struct cxl_decoder *cxl_decoder_alloc(struct cxl_port *port, cxld->id = rc; cxld->nr_targets = nr_targets; + seqlock_init(&cxld->target_lock); dev = &cxld->dev; device_initialize(dev); device_set_pm_not_required(dev); diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h index 6a38d2e1f3dd..e79162999088 100644 --- a/drivers/cxl/cxl.h +++ b/drivers/cxl/cxl.h @@ -185,6 +185,7 @@ enum cxl_decoder_type { * @interleave_granularity: data stride per dport * @target_type: accelerator vs expander (type2 vs type3) selector * @flags: memory type capabilities and locking + * @target_lock: coordinate coherent reads of the target list * @nr_targets: number of elements in @target * @target: active ordered target list in current decoder configuration */ @@ -199,6 +200,7 @@ struct cxl_decoder { int interleave_granularity; enum cxl_decoder_type target_type; unsigned long flags; + seqlock_t target_lock; int nr_targets; struct cxl_dport *target[]; }; -- cgit v1.2.3-59-g8ed1b