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Date: Thu, 20 Sep 2018 15:45:38 +0300
From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Mathieu Poirier <mathieu.poirier@...aro.org>
Cc: linux-kernel@...r.kernel.org,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: [QUEUED v20180920 01/16] stm class: Rework policy node fallback
Currently, if no matching policy node can be found for a trace source,
we'll try to use "default" policy node, then, if that doesn't exist,
we'll pick the first node, in order of creation. If that also fails,
we'll allocate M/C range from the beginning of the device's M/C range.
This makes it difficult to know which node (if any) was used in any
particular case.
In order to make things more deterministic, the new order is as follows:
* if they supply ID string, use that and nothing else,
* if they are a task, use their task name (comm),
* use "default", if it exists,
* return failure, to let them know there is no suitable rule.
This should provide enough convenience with the "default" catch-all node,
while not leaving *everything* to chance. As a side effect, this relaxes
the requirement of using ioctl() for identification with the possibility of
using task names as policy nodes.
Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
---
drivers/hwtracing/stm/core.c | 89 ++++++++++++++++++++--------------
drivers/hwtracing/stm/policy.c | 12 ++---
drivers/hwtracing/stm/stm.h | 2 -
3 files changed, 58 insertions(+), 45 deletions(-)
diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index 10bcb5d73f90..7b1c549d6320 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -293,15 +293,15 @@ static int stm_output_assign(struct stm_device *stm, unsigned int width,
if (width > stm->data->sw_nchannels)
return -EINVAL;
- if (policy_node) {
- stp_policy_node_get_ranges(policy_node,
- &midx, &mend, &cidx, &cend);
- } else {
- midx = stm->data->sw_start;
- cidx = 0;
- mend = stm->data->sw_end;
- cend = stm->data->sw_nchannels - 1;
- }
+ /* We no longer accept policy_node==NULL here */
+ if (WARN_ON_ONCE(!policy_node))
+ return -EINVAL;
+
+ /*
+ * Also, the caller holds reference to policy_node, so it won't
+ * disappear on us.
+ */
+ stp_policy_node_get_ranges(policy_node, &midx, &mend, &cidx, &cend);
spin_lock(&stm->mc_lock);
spin_lock(&output->lock);
@@ -405,19 +405,30 @@ static int stm_char_release(struct inode *inode, struct file *file)
return 0;
}
-static int stm_file_assign(struct stm_file *stmf, char *id, unsigned int width)
+static int
+stm_assign_first_policy(struct stm_device *stm, struct stm_output *output,
+ char **ids, unsigned int width)
{
- struct stm_device *stm = stmf->stm;
- int ret;
+ struct stp_policy_node *pn;
+ int err, n;
- stmf->policy_node = stp_policy_node_lookup(stm, id);
+ /*
+ * On success, stp_policy_node_lookup() will return holding the
+ * configfs subsystem mutex, which is then released in
+ * stp_policy_node_put(). This allows the pdrv->output_open() in
+ * stm_output_assign() to serialize against the attribute accessors.
+ */
+ for (n = 0, pn = NULL; ids[n] && !pn; n++)
+ pn = stp_policy_node_lookup(stm, ids[n]);
- ret = stm_output_assign(stm, width, stmf->policy_node, &stmf->output);
+ if (!pn)
+ return -EINVAL;
- if (stmf->policy_node)
- stp_policy_node_put(stmf->policy_node);
+ err = stm_output_assign(stm, width, pn, output);
- return ret;
+ stp_policy_node_put(pn);
+
+ return err;
}
static ssize_t notrace stm_write(struct stm_data *data, unsigned int master,
@@ -455,16 +466,23 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
count = PAGE_SIZE - 1;
/*
- * if no m/c have been assigned to this writer up to this
- * point, use "default" policy entry
+ * If no m/c have been assigned to this writer up to this
+ * point, try to use the task name and "default" policy entries.
*/
if (!stmf->output.nr_chans) {
- err = stm_file_assign(stmf, "default", 1);
+ char comm[sizeof(current->comm)];
+ char *ids[] = { comm, "default", NULL };
+
+ get_task_comm(comm, current);
+
+ err = stm_assign_first_policy(stmf->stm, &stmf->output, ids, 1);
/*
* EBUSY means that somebody else just assigned this
- * output, which is just fine for write()
+ * output, which is just fine for write(), except for (XXX)
+ * it doesn't actually return -EBUSY, but -EINVAL and WARNs
+ * in this case. Hrrr.
*/
- if (err && err != -EBUSY)
+ if (err)
return err;
}
@@ -550,6 +568,7 @@ static int stm_char_policy_set_ioctl(struct stm_file *stmf, void __user *arg)
{
struct stm_device *stm = stmf->stm;
struct stp_policy_id *id;
+ char *ids[] = { NULL, NULL };
int ret = -EINVAL;
u32 size;
@@ -582,7 +601,9 @@ static int stm_char_policy_set_ioctl(struct stm_file *stmf, void __user *arg)
id->width > PAGE_SIZE / stm->data->sw_mmiosz)
goto err_free;
- ret = stm_file_assign(stmf, id->id, id->width);
+ ids[0] = id->id;
+ ret = stm_assign_first_policy(stmf->stm, &stmf->output, ids,
+ id->width);
if (ret)
goto err_free;
@@ -818,8 +839,8 @@ EXPORT_SYMBOL_GPL(stm_unregister_device);
static int stm_source_link_add(struct stm_source_device *src,
struct stm_device *stm)
{
- char *id;
- int err;
+ char *ids[] = { NULL, "default", NULL };
+ int err = -ENOMEM;
mutex_lock(&stm->link_mutex);
spin_lock(&stm->link_lock);
@@ -833,19 +854,13 @@ static int stm_source_link_add(struct stm_source_device *src,
spin_unlock(&stm->link_lock);
mutex_unlock(&stm->link_mutex);
- id = kstrdup(src->data->name, GFP_KERNEL);
- if (id) {
- src->policy_node =
- stp_policy_node_lookup(stm, id);
-
- kfree(id);
- }
-
- err = stm_output_assign(stm, src->data->nr_chans,
- src->policy_node, &src->output);
+ ids[0] = kstrdup(src->data->name, GFP_KERNEL);
+ if (!ids[0])
+ goto fail_detach;
- if (src->policy_node)
- stp_policy_node_put(src->policy_node);
+ err = stm_assign_first_policy(stm, &src->output, ids,
+ src->data->nr_chans);
+ kfree(ids[0]);
if (err)
goto fail_detach;
diff --git a/drivers/hwtracing/stm/policy.c b/drivers/hwtracing/stm/policy.c
index 3fd07e275b34..15d35d891643 100644
--- a/drivers/hwtracing/stm/policy.c
+++ b/drivers/hwtracing/stm/policy.c
@@ -392,7 +392,7 @@ static struct configfs_subsystem stp_policy_subsys = {
static struct stp_policy_node *
__stp_policy_node_lookup(struct stp_policy *policy, char *s)
{
- struct stp_policy_node *policy_node, *ret;
+ struct stp_policy_node *policy_node, *ret = NULL;
struct list_head *head = &policy->group.cg_children;
struct config_item *item;
char *start, *end = s;
@@ -400,10 +400,6 @@ __stp_policy_node_lookup(struct stp_policy *policy, char *s)
if (list_empty(head))
return NULL;
- /* return the first entry if everything else fails */
- item = list_entry(head->next, struct config_item, ci_entry);
- ret = to_stp_policy_node(item);
-
next:
for (;;) {
start = strsep(&end, "/");
@@ -449,13 +445,17 @@ stp_policy_node_lookup(struct stm_device *stm, char *s)
if (policy_node)
config_item_get(&policy_node->group.cg_item);
- mutex_unlock(&stp_policy_subsys.su_mutex);
+ else
+ mutex_unlock(&stp_policy_subsys.su_mutex);
return policy_node;
}
void stp_policy_node_put(struct stp_policy_node *policy_node)
{
+ lockdep_assert_held(&stp_policy_subsys.su_mutex);
+
+ mutex_unlock(&stp_policy_subsys.su_mutex);
config_item_put(&policy_node->group.cg_item);
}
diff --git a/drivers/hwtracing/stm/stm.h b/drivers/hwtracing/stm/stm.h
index 923571adc6f4..e5df08ae59cf 100644
--- a/drivers/hwtracing/stm/stm.h
+++ b/drivers/hwtracing/stm/stm.h
@@ -57,7 +57,6 @@ struct stm_output {
struct stm_file {
struct stm_device *stm;
- struct stp_policy_node *policy_node;
struct stm_output output;
};
@@ -71,7 +70,6 @@ struct stm_source_device {
struct stm_device __rcu *link;
struct list_head link_entry;
/* one output per stm_source device */
- struct stp_policy_node *policy_node;
struct stm_output output;
};
--
2.18.0
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