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cxl/core/port: Use dedicated lock for decoder target list

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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 <ben.widawsky@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/164367209095.208169.1171673319121271280.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Dan Williams 2022-01-31 15:35:18 -08:00
parent 3c5b903955
commit 86c8ea0f3b
2 changed files with 25 additions and 7 deletions
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30
drivers/cxl/core/port.c
View File

@ -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);

2
drivers/cxl/cxl.h
View File

@ -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[];
};