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Subject[PATCH 11/31] CAPI: Rework application locking
Drop the application rw-lock in favour of RCU. This synchronizes
capi20_release against capi_ctr_handle_message which may dereference an
application from (soft-)IRQ context. Any other access to the application
list is now protected by the capi_controller_lock as well. This also
allows to safely inspect applications for /proc dumping by holding
capi_controller_lock.

At this chance, drop some useless release_in_progress checks where we
obtained the application pointer from the list (which becomes NULL on
release_in_progress).

Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
---
drivers/isdn/capi/kcapi.c | 52 +++++++++++++++++-----------------------
drivers/isdn/capi/kcapi_proc.c | 11 +++++---
2 files changed, 29 insertions(+), 34 deletions(-)
diff --git a/drivers/isdn/capi/kcapi.c b/drivers/isdn/capi/kcapi.c
index 964650a..2c5d1b8 100644
--- a/drivers/isdn/capi/kcapi.c
+++ b/drivers/isdn/capi/kcapi.c
@@ -34,6 +34,7 @@
#include <linux/b1lli.h>
#endif
#include <linux/mutex.h>
+#include <linux/rcupdate.h>

static int showcapimsgs = 0;

@@ -64,8 +65,6 @@ DEFINE_MUTEX(capi_drivers_lock);
struct capi_ctr *capi_controller[CAPI_MAXCONTR];
DEFINE_MUTEX(capi_controller_lock);

-static DEFINE_RWLOCK(application_lock);
-
struct capi20_appl *capi_applications[CAPI_MAXAPPL];

static int ncontrollers;
@@ -103,7 +102,7 @@ static inline struct capi20_appl *get_capi_appl_by_nr(u16 applid)
if (applid - 1 >= CAPI_MAXAPPL)
return NULL;

- return capi_applications[applid - 1];
+ return rcu_dereference(capi_applications[applid - 1]);
}

/* -------- util functions ------------------------------------ */
@@ -186,7 +185,7 @@ static void notify_up(u32 contr)

for (applid = 1; applid <= CAPI_MAXAPPL; applid++) {
ap = get_capi_appl_by_nr(applid);
- if (!ap || ap->release_in_progress)
+ if (!ap)
continue;
register_appl(ctr, applid, &ap->rparam);
}
@@ -214,7 +213,7 @@ static void ctr_down(struct capi_ctr *ctr)

for (applid = 1; applid <= CAPI_MAXAPPL; applid++) {
ap = get_capi_appl_by_nr(applid);
- if (ap && !ap->release_in_progress)
+ if (ap)
capi_ctr_put(ctr);
}
}
@@ -332,7 +331,6 @@ void capi_ctr_handle_message(struct capi_ctr *ctr, u16 appl,
struct capi20_appl *ap;
int showctl = 0;
u8 cmd, subcmd;
- unsigned long flags;
_cdebbuf *cdb;

if (ctr->state != CAPI_CTR_RUNNING) {
@@ -380,10 +378,10 @@ void capi_ctr_handle_message(struct capi_ctr *ctr, u16 appl,

}

- read_lock_irqsave(&application_lock, flags);
+ rcu_read_lock();
ap = get_capi_appl_by_nr(CAPIMSG_APPID(skb->data));
- if ((!ap) || (ap->release_in_progress)) {
- read_unlock_irqrestore(&application_lock, flags);
+ if (!ap) {
+ rcu_read_unlock();
cdb = capi_message2str(skb->data);
if (cdb) {
printk(KERN_ERR "kcapi: handle_message: applid %d state released (%s)n",
@@ -397,7 +395,7 @@ void capi_ctr_handle_message(struct capi_ctr *ctr, u16 appl,
}
skb_queue_tail(&ap->recv_queue, skb);
schedule_work(&ap->recv_work);
- read_unlock_irqrestore(&application_lock, flags);
+ rcu_read_unlock();

return;

@@ -649,40 +647,35 @@ u16 capi20_register(struct capi20_appl *ap)
{
int i;
u16 applid;
- unsigned long flags;

DBG("");

if (ap->rparam.datablklen < 128)
return CAPI_LOGBLKSIZETOSMALL;

- write_lock_irqsave(&application_lock, flags);
+ ap->nrecvctlpkt = 0;
+ ap->nrecvdatapkt = 0;
+ ap->nsentctlpkt = 0;
+ ap->nsentdatapkt = 0;
+ mutex_init(&ap->recv_mtx);
+ skb_queue_head_init(&ap->recv_queue);
+ INIT_WORK(&ap->recv_work, recv_handler);
+ ap->release_in_progress = 0;
+
+ mutex_lock(&capi_controller_lock);

for (applid = 1; applid <= CAPI_MAXAPPL; applid++) {
if (capi_applications[applid - 1] == NULL)
break;
}
if (applid > CAPI_MAXAPPL) {
- write_unlock_irqrestore(&application_lock, flags);
+ mutex_unlock(&capi_controller_lock);
return CAPI_TOOMANYAPPLS;
}

ap->applid = applid;
capi_applications[applid - 1] = ap;

- ap->nrecvctlpkt = 0;
- ap->nrecvdatapkt = 0;
- ap->nsentctlpkt = 0;
- ap->nsentdatapkt = 0;
- mutex_init(&ap->recv_mtx);
- skb_queue_head_init(&ap->recv_queue);
- INIT_WORK(&ap->recv_work, recv_handler);
- ap->release_in_progress = 0;
-
- write_unlock_irqrestore(&application_lock, flags);
-
- mutex_lock(&capi_controller_lock);
-
for (i = 0; i < CAPI_MAXCONTR; i++) {
if (!capi_controller[i] ||
capi_controller[i]->state != CAPI_CTR_RUNNING)
@@ -714,16 +707,15 @@ EXPORT_SYMBOL(capi20_register);
u16 capi20_release(struct capi20_appl *ap)
{
int i;
- unsigned long flags;

DBG("applid %#x", ap->applid);

- write_lock_irqsave(&application_lock, flags);
+ mutex_lock(&capi_controller_lock);
+
ap->release_in_progress = 1;
capi_applications[ap->applid - 1] = NULL;
- write_unlock_irqrestore(&application_lock, flags);

- mutex_lock(&capi_controller_lock);
+ synchronize_rcu();

for (i = 0; i < CAPI_MAXCONTR; i++) {
if (!capi_controller[i] ||
diff --git a/drivers/isdn/capi/kcapi_proc.c b/drivers/isdn/capi/kcapi_proc.c
index 3e6e17a..ea2dff6 100644
--- a/drivers/isdn/capi/kcapi_proc.c
+++ b/drivers/isdn/capi/kcapi_proc.c
@@ -139,9 +139,11 @@ static const struct file_operations proc_contrstats_ops = {
// applid nrecvctlpkt nrecvdatapkt nsentctlpkt nsentdatapkt
// ---------------------------------------------------------------------------

-static void *
-applications_start(struct seq_file *seq, loff_t *pos)
+static void *applications_start(struct seq_file *seq, loff_t *pos)
+ __acquires(capi_controller_lock)
{
+ mutex_lock(&capi_controller_lock);
+
if (*pos < CAPI_MAXAPPL)
return &capi_applications[*pos];

@@ -158,9 +160,10 @@ applications_next(struct seq_file *seq, void *v, loff_t *pos)
return NULL;
}

-static void
-applications_stop(struct seq_file *seq, void *v)
+static void applications_stop(struct seq_file *seq, void *v)
+ __releases(capi_controller_lock)
{
+ mutex_unlock(&capi_controller_lock);
}

static int
--
1.6.0.2


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