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Make kstat.ks_update() callback atomic

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Move the kstat ks_update() callback under the ks_lock.  This
enables dynamically sized kstats without modification to the
kstat API.

  * Create a kstat with the KSTAT_FLAG_VIRTUAL flag.
  * Register a ->ks_update() callback which does:
    o Frees any existing ks_data buffer.
    o Set ks_data_size to the kstat array size.
    o Set ks_data to an allocated buffer of size ks_data_size
    o Populate the array of buffers with the required data.

The buffer allocated in the ks_update() callback is guaranteed
to remain allocated and valid while the proc sequence handler
iterates over the buffer.  The lock will not be dropped until
kstat_seq_stop() function is run making it safe for concurrent
access.  To allow the ks_update() callback to perform memory
allocations the lock was changed to a mutex.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This commit is contained in:
Brian Behlendorf 2012-10-23 09:17:29 -07:00
parent 1e0c2c2ccf
commit 71c9f0b003
2 changed files with 9 additions and 6 deletions
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3
include/sys/kstat.h
View File

@ -30,6 +30,7 @@
#include <sys/types.h>
#include <sys/time.h>
#include <sys/kmem.h>
#include <sys/mutex.h>
#define KSTAT_STRLEN 31
@ -98,7 +99,7 @@ typedef struct kstat_s {
struct proc_dir_entry *ks_proc; /* proc linkage */
kstat_update_t *ks_update; /* dynamic updates */
void *ks_private; /* private data */
spinlock_t ks_lock; /* kstat data lock */
kmutex_t ks_lock; /* kstat data lock */
struct list_head ks_list; /* kstat linkage */
} kstat_t;

12
module/spl/spl-kstat.c
View File

@ -267,10 +267,11 @@ kstat_seq_start(struct seq_file *f, loff_t *pos)
ASSERT(ksp->ks_magic == KS_MAGIC);
SENTRY;
mutex_enter(&ksp->ks_lock);
/* Dynamically update kstat, on error existing kstats are used */
(void) ksp->ks_update(ksp, KSTAT_READ);
spin_lock(&ksp->ks_lock);
ksp->ks_snaptime = gethrtime();
if (!n)
@ -302,7 +303,7 @@ kstat_seq_stop(struct seq_file *f, void *v)
kstat_t *ksp = (kstat_t *)f->private;
ASSERT(ksp->ks_magic == KS_MAGIC);
spin_unlock(&ksp->ks_lock);
mutex_exit(&ksp->ks_lock);
}
static struct seq_operations kstat_seq_ops = {
@ -360,7 +361,7 @@ __kstat_create(const char *ks_module, int ks_instance, const char *ks_name,
spin_unlock(&kstat_lock);
ksp->ks_magic = KS_MAGIC;
spin_lock_init(&ksp->ks_lock);
mutex_init(&ksp->ks_lock, NULL, MUTEX_DEFAULT, NULL);
INIT_LIST_HEAD(&ksp->ks_list);
ksp->ks_crtime = gethrtime();
@ -445,11 +446,11 @@ __kstat_install(kstat_t *ksp)
if (de_name == NULL)
SGOTO(out, rc = -EUNATCH);
spin_lock(&ksp->ks_lock);
mutex_enter(&ksp->ks_lock);
ksp->ks_proc = de_name;
de_name->proc_fops = &proc_kstat_operations;
de_name->data = (void *)ksp;
spin_unlock(&ksp->ks_lock);
mutex_exit(&ksp->ks_lock);
out:
if (rc) {
spin_lock(&kstat_lock);
@ -482,6 +483,7 @@ __kstat_delete(kstat_t *ksp)
if (!(ksp->ks_flags & KSTAT_FLAG_VIRTUAL))
kmem_free(ksp->ks_data, ksp->ks_data_size);
mutex_destroy(&ksp->ks_lock);
kmem_free(ksp, sizeof(*ksp));
return;