Now the output of io cgroup name in blktrace is controlled by
blk_cgroup & blk_cgname options in trace_options files. When
using cgroup v1 for io controller, there is no output of cgroup
name in trace file, because cgroup_path_from_kernfs_id() uses
cgrp_dfl_root.kf_root to find the cgroup file and cgrp_dfl_root
is only valid for cgroup v2.
So fix cgroup_path_from_kernfs_id() to support both cgroup v1 and v2.
Fixes: 69fd5c3 ("blktrace: add an option to allow displaying cgroup path")
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
include/linux/cgroup.h | 6 +++---
kernel/cgroup/cgroup.c | 39 ++++++++++++++++++++++++++++++++++++---
kernel/trace/blktrace.c | 4 ++--
3 files changed, 41 insertions(+), 8 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 473e0c0..ed80490 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -651,7 +651,7 @@ static inline union kernfs_node_id *cgroup_get_kernfs_id(struct cgroup *cgrp)
return &cgrp->kn->id;
}
-void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
+void cgroup_path_from_kernfs_id(int ssid, const union kernfs_node_id *id,
char *buf, size_t buflen);
#else /* !CONFIG_CGROUPS */
@@ -686,8 +686,8 @@ static inline bool task_under_cgroup_hierarchy(struct task_struct *task,
return true;
}
-static inline void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
- char *buf, size_t buflen) {}
+static inline void cgroup_path_from_kernfs_id(int ssid,
+ const union kernfs_node_id *id, char *buf, size_t buflen) {}
#endif /* !CONFIG_CGROUPS */
/*
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 0b1ffe1..49d63c6 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5354,16 +5354,49 @@ static int __init cgroup_wq_init(void)
}
core_initcall(cgroup_wq_init);
-void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
+void cgroup_path_from_kernfs_id(int ssid, const union kernfs_node_id *id,
char *buf, size_t buflen)
{
+ struct kernfs_root *root;
struct kernfs_node *kn;
+ struct cgroup *root_cgrp = NULL;
- kn = kernfs_get_node_by_id(cgrp_dfl_root.kf_root, id);
- if (!kn)
+ if (ssid >= CGROUP_SUBSYS_COUNT)
return;
+
+ if (likely(static_key_enabled(cgroup_subsys_on_dfl_key[ssid]))) {
+ root = cgrp_dfl_root.kf_root;
+ } else {
+ struct cgroup_subsys *subsys = cgroup_subsys[ssid];
+
+ /*
+ * It seems we can not use rcu_read_lock() to protect
+ * the liveness check of subsys->root->cgrp. Although
+ * root->cgrp is freed by RCU, when we dereference the
+ * old root, the old root may been destroying by
+ * cgroup_destroy_root().
+ */
+ mutex_lock(&cgroup_mutex);
+ if (percpu_ref_tryget_live(&subsys->root->cgrp.self.refcnt)) {
+ root_cgrp = &subsys->root->cgrp;
+ root = subsys->root->kf_root;
+ }
+ mutex_unlock(&cgroup_mutex);
+
+ if (!root_cgrp)
+ goto out;
+ }
+
+ kn = kernfs_get_node_by_id(root, id);
+ if (!kn)
+ goto out;
+
kernfs_path(kn, buf, buflen);
kernfs_put(kn);
+
+out:
+ if (root_cgrp)
+ cgroup_put(root_cgrp);
}
/*
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 987d9a9a..79890e0 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -1279,8 +1279,8 @@ static void blk_log_action(struct trace_iterator *iter, const char *act,
if (blk_tracer_flags.val & TRACE_BLK_OPT_CGNAME) {
char blkcg_name_buf[NAME_MAX + 1] = "<...>";
- cgroup_path_from_kernfs_id(id, blkcg_name_buf,
- sizeof(blkcg_name_buf));
+ cgroup_path_from_kernfs_id(io_cgrp_id, id,
+ blkcg_name_buf, sizeof(blkcg_name_buf));
trace_seq_printf(&iter->seq, "%3d,%-3d %s %2s %3s ",
MAJOR(t->device), MINOR(t->device),
blkcg_name_buf, act, rwbs);
--
2.9.5
--
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