Hi Alex, On Thu, Sep 20, 2018 at 03:45:38PM +0300, Alexander Shishkin wrote: > 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.
I am good with the "default" catch all clause but the change in behaviour has to be documented. Otherwise people can be mislead in thinking that a regression has happened. Before this patch: root@nano:~# mkdir /sys/kernel/config/stp-policy/20100000.stm.test root@nano:~# echo 20100000.stm > /sys/class/stm_source/ftrace/stm_source_link root@linaro-nano:~# cat /sys/class/stm_source/ftrace/stm_source_link 20100000.stm After this patch: root@nano:~# mkdir /sys/kernel/config/stp-policy/20100000.stm.test root@nano:~# echo 20100000.stm > /sys/class/stm_source/ftrace/stm_source_link bash: echo: write error: Invalid argument root@nano:~# mkdir /sys/kernel/config/stp-policy/20100000.stm.test/default root@nano:~# echo 20100000.stm > /sys/class/stm_source/ftrace/stm_source_link root@linaro-nano:~# cat /sys/class/stm_source/ftrace/stm_source_link 20100000.stm > > 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 <[email protected]> > --- > 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 >
