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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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