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https://github.com/brain-hackers/linux-brain.git
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tracepoint: simplification for tracepoints using RCU
Impact: simplify implementation
Now, unused memory is handled by struct tp_probes.
old code use these three field to handle unused memory.
struct tracepoint_entry {
...
struct rcu_head rcu;
void *oldptr;
unsigned char rcu_pending:1;
...
};
in this way, unused memory is handled by struct tracepoint_entry.
it bring reenter bug(it was fixed) and tracepoint.c is filled
full of ".*rcu.*" code statements. this patch removes all these.
and:
rcu_barrier_sched() is removed.
Do not need regain tracepoints_mutex after tracepoint_update_probes()
several little cleanup.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Lai Jiangshan
Ingo Molnar
parent
45beca08dd
commit
19dba33c43
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@ -43,6 +43,7 @@ static DEFINE_MUTEX(tracepoints_mutex);
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*/
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#define TRACEPOINT_HASH_BITS 6
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#define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
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static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
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/*
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* Note about RCU :
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@ -54,40 +55,40 @@ struct tracepoint_entry {
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struct hlist_node hlist;
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void **funcs;
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int refcount; /* Number of times armed. 0 if disarmed. */
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struct rcu_head rcu;
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void *oldptr;
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unsigned char rcu_pending:1;
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char name[0];
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};
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static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
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struct tp_probes {
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struct rcu_head rcu;
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void *probes[0];
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};
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static void free_old_closure(struct rcu_head *head)
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static inline void *allocate_probes(int count)
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{
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struct tracepoint_entry *entry = container_of(head,
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struct tracepoint_entry, rcu);
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kfree(entry->oldptr);
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/* Make sure we free the data before setting the pending flag to 0 */
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smp_wmb();
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entry->rcu_pending = 0;
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struct tp_probes *p = kmalloc(count * sizeof(void *)
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+ sizeof(struct tp_probes), GFP_KERNEL);
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return p == NULL ? NULL : p->probes;
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}
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static void tracepoint_entry_free_old(struct tracepoint_entry *entry, void *old)
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static void rcu_free_old_probes(struct rcu_head *head)
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{
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if (!old)
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return;
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entry->oldptr = old;
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entry->rcu_pending = 1;
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/* write rcu_pending before calling the RCU callback */
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smp_wmb();
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call_rcu_sched(&entry->rcu, free_old_closure);
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kfree(container_of(head, struct tp_probes, rcu));
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}
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static inline void release_probes(void *old)
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{
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if (old) {
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struct tp_probes *tp_probes = container_of(old,
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struct tp_probes, probes[0]);
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call_rcu(&tp_probes->rcu, rcu_free_old_probes);
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}
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}
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static void debug_print_probes(struct tracepoint_entry *entry)
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{
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int i;
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if (!tracepoint_debug)
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if (!tracepoint_debug || !entry->funcs)
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return;
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for (i = 0; entry->funcs[i]; i++)
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@ -111,12 +112,13 @@ tracepoint_entry_add_probe(struct tracepoint_entry *entry, void *probe)
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return ERR_PTR(-EEXIST);
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}
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/* + 2 : one for new probe, one for NULL func */
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new = kzalloc((nr_probes + 2) * sizeof(void *), GFP_KERNEL);
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new = allocate_probes(nr_probes + 2);
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if (new == NULL)
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return ERR_PTR(-ENOMEM);
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if (old)
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memcpy(new, old, nr_probes * sizeof(void *));
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new[nr_probes] = probe;
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new[nr_probes + 1] = NULL;
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entry->refcount = nr_probes + 1;
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entry->funcs = new;
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debug_print_probes(entry);
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@ -132,7 +134,7 @@ tracepoint_entry_remove_probe(struct tracepoint_entry *entry, void *probe)
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old = entry->funcs;
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if (!old)
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return NULL;
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return ERR_PTR(-ENOENT);
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debug_print_probes(entry);
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/* (N -> M), (N > 1, M >= 0) probes */
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@ -151,13 +153,13 @@ tracepoint_entry_remove_probe(struct tracepoint_entry *entry, void *probe)
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int j = 0;
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/* N -> M, (N > 1, M > 0) */
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/* + 1 for NULL */
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new = kzalloc((nr_probes - nr_del + 1)
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* sizeof(void *), GFP_KERNEL);
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new = allocate_probes(nr_probes - nr_del + 1);
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if (new == NULL)
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return ERR_PTR(-ENOMEM);
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for (i = 0; old[i]; i++)
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if ((probe && old[i] != probe))
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new[j++] = old[i];
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new[nr_probes - nr_del] = NULL;
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entry->refcount = nr_probes - nr_del;
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entry->funcs = new;
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}
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@ -215,7 +217,6 @@ static struct tracepoint_entry *add_tracepoint(const char *name)
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memcpy(&e->name[0], name, name_len);
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e->funcs = NULL;
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e->refcount = 0;
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e->rcu_pending = 0;
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hlist_add_head(&e->hlist, head);
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return e;
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}
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@ -224,32 +225,10 @@ static struct tracepoint_entry *add_tracepoint(const char *name)
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* Remove the tracepoint from the tracepoint hash table. Must be called with
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* mutex_lock held.
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*/
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static int remove_tracepoint(const char *name)
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static inline void remove_tracepoint(struct tracepoint_entry *e)
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{
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struct hlist_head *head;
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struct hlist_node *node;
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struct tracepoint_entry *e;
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int found = 0;
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size_t len = strlen(name) + 1;
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u32 hash = jhash(name, len-1, 0);
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head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
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hlist_for_each_entry(e, node, head, hlist) {
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if (!strcmp(name, e->name)) {
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found = 1;
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break;
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}
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}
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if (!found)
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return -ENOENT;
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if (e->refcount)
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return -EBUSY;
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hlist_del(&e->hlist);
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/* Make sure the call_rcu_sched has been executed */
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if (e->rcu_pending)
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rcu_barrier_sched();
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kfree(e);
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return 0;
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}
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/*
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@ -343,25 +322,17 @@ int tracepoint_probe_register(const char *name, void *probe)
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goto end;
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}
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}
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/*
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* If we detect that a call_rcu_sched is pending for this tracepoint,
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* make sure it's executed now.
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*/
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if (entry->rcu_pending)
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rcu_barrier_sched();
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old = tracepoint_entry_add_probe(entry, probe);
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if (IS_ERR(old)) {
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if (!entry->refcount)
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remove_tracepoint(entry);
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ret = PTR_ERR(old);
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goto end;
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}
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mutex_unlock(&tracepoints_mutex);
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tracepoint_update_probes(); /* may update entry */
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mutex_lock(&tracepoints_mutex);
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entry = get_tracepoint(name);
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WARN_ON(!entry);
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if (entry->rcu_pending)
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rcu_barrier_sched();
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tracepoint_entry_free_old(entry, old);
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release_probes(old);
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return 0;
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end:
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mutex_unlock(&tracepoints_mutex);
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return ret;
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@ -388,25 +359,17 @@ int tracepoint_probe_unregister(const char *name, void *probe)
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entry = get_tracepoint(name);
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if (!entry)
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goto end;
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if (entry->rcu_pending)
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rcu_barrier_sched();
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old = tracepoint_entry_remove_probe(entry, probe);
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if (!old) {
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printk(KERN_WARNING "Warning: Trying to unregister a probe"
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"that doesn't exist\n");
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if (IS_ERR(old)) {
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ret = PTR_ERR(old);
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goto end;
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}
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if (!entry->refcount)
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remove_tracepoint(entry);
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mutex_unlock(&tracepoints_mutex);
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tracepoint_update_probes(); /* may update entry */
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mutex_lock(&tracepoints_mutex);
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entry = get_tracepoint(name);
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if (!entry)
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goto end;
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if (entry->rcu_pending)
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rcu_barrier_sched();
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tracepoint_entry_free_old(entry, old);
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remove_tracepoint(name); /* Ignore busy error message */
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ret = 0;
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release_probes(old);
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return 0;
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end:
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mutex_unlock(&tracepoints_mutex);
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return ret;
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