]> git.karo-electronics.de Git - karo-tx-linux.git/blobdiff - kernel/trace/blktrace.c
blktrace: support per-partition tracing
[karo-tx-linux.git] / kernel / trace / blktrace.c
index 6fb274f5f34e47219ed5d5af45bbdf279364bf02..e932654cf5900662021abaf8573c3151ac5c8581 100644 (file)
@@ -59,22 +59,39 @@ static void trace_note(struct blk_trace *bt, pid_t pid, int action,
                       const void *data, size_t len)
 {
        struct blk_io_trace *t;
+       struct ring_buffer_event *event = NULL;
+       int pc = 0;
+       int cpu = smp_processor_id();
+       bool blk_tracer = blk_tracer_enabled;
+
+       if (blk_tracer) {
+               pc = preempt_count();
+               event = trace_buffer_lock_reserve(blk_tr, TRACE_BLK,
+                                                 sizeof(*t) + len,
+                                                 0, pc);
+               if (!event)
+                       return;
+               t = ring_buffer_event_data(event);
+               goto record_it;
+       }
 
        if (!bt->rchan)
                return;
 
        t = relay_reserve(bt->rchan, sizeof(*t) + len);
        if (t) {
-               const int cpu = smp_processor_id();
-
                t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
                t->time = ktime_to_ns(ktime_get());
+record_it:
                t->device = bt->dev;
                t->action = action;
                t->pid = pid;
                t->cpu = cpu;
                t->pdu_len = len;
                memcpy((void *) t + sizeof(*t), data, len);
+
+               if (blk_tracer)
+                       trace_buffer_unlock_commit(blk_tr, event, 0, pc);
        }
 }
 
@@ -110,14 +127,8 @@ void __trace_note_message(struct blk_trace *bt, const char *fmt, ...)
        unsigned long flags;
        char *buf;
 
-       if (blk_tr) {
-               va_start(args, fmt);
-               ftrace_vprintk(fmt, args);
-               va_end(args);
-               return;
-       }
-
-       if (!bt->msg_data)
+       if (unlikely(bt->trace_state != Blktrace_running &&
+                    !blk_tracer_enabled))
                return;
 
        local_irq_save(flags);
@@ -136,7 +147,7 @@ static int act_log_check(struct blk_trace *bt, u32 what, sector_t sector,
 {
        if (((bt->act_mask << BLK_TC_SHIFT) & what) == 0)
                return 1;
-       if (sector < bt->start_lba || sector > bt->end_lba)
+       if (sector && (sector < bt->start_lba || sector > bt->end_lba))
                return 1;
        if (bt->pid && pid != bt->pid)
                return 1;
@@ -168,9 +179,9 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
        unsigned long *sequence;
        pid_t pid;
        int cpu, pc = 0;
+       bool blk_tracer = blk_tracer_enabled;
 
-       if (unlikely(bt->trace_state != Blktrace_running ||
-                    !blk_tracer_enabled))
+       if (unlikely(bt->trace_state != Blktrace_running && !blk_tracer))
                return;
 
        what |= ddir_act[rw & WRITE];
@@ -181,11 +192,11 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
        what |= MASK_TC_BIT(rw, DISCARD);
 
        pid = tsk->pid;
-       if (unlikely(act_log_check(bt, what, sector, pid)))
+       if (act_log_check(bt, what, sector, pid))
                return;
        cpu = raw_smp_processor_id();
 
-       if (blk_tr) {
+       if (blk_tracer) {
                tracing_record_cmdline(current);
 
                pc = preempt_count();
@@ -235,7 +246,7 @@ record_it:
                if (pdu_len)
                        memcpy((void *) t + sizeof(*t), pdu_data, pdu_len);
 
-               if (blk_tr) {
+               if (blk_tracer) {
                        trace_buffer_unlock_commit(blk_tr, event, 0, pc);
                        return;
                }
@@ -247,7 +258,7 @@ record_it:
 static struct dentry *blk_tree_root;
 static DEFINE_MUTEX(blk_tree_mutex);
 
-static void blk_trace_cleanup(struct blk_trace *bt)
+static void blk_trace_free(struct blk_trace *bt)
 {
        debugfs_remove(bt->msg_file);
        debugfs_remove(bt->dropped_file);
@@ -255,6 +266,11 @@ static void blk_trace_cleanup(struct blk_trace *bt)
        free_percpu(bt->sequence);
        free_percpu(bt->msg_data);
        kfree(bt);
+}
+
+static void blk_trace_cleanup(struct blk_trace *bt)
+{
+       blk_trace_free(bt);
        if (atomic_dec_and_test(&blk_probes_ref))
                blk_unregister_tracepoints();
 }
@@ -267,8 +283,7 @@ int blk_trace_remove(struct request_queue *q)
        if (!bt)
                return -EINVAL;
 
-       if (bt->trace_state == Blktrace_setup ||
-           bt->trace_state == Blktrace_stopped)
+       if (bt->trace_state != Blktrace_running)
                blk_trace_cleanup(bt);
 
        return 0;
@@ -312,10 +327,10 @@ static ssize_t blk_msg_write(struct file *filp, const char __user *buffer,
        char *msg;
        struct blk_trace *bt;
 
-       if (count > BLK_TN_MAX_MSG)
+       if (count >= BLK_TN_MAX_MSG)
                return -EINVAL;
 
-       msg = kmalloc(count, GFP_KERNEL);
+       msg = kmalloc(count + 1, GFP_KERNEL);
        if (msg == NULL)
                return -ENOMEM;
 
@@ -324,6 +339,7 @@ static ssize_t blk_msg_write(struct file *filp, const char __user *buffer,
                return -EFAULT;
        }
 
+       msg[count] = '\0';
        bt = filp->private_data;
        __trace_note_message(bt, "%s", msg);
        kfree(msg);
@@ -391,11 +407,13 @@ static struct rchan_callbacks blk_relay_callbacks = {
  * Setup everything required to start tracing
  */
 int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
-                       struct blk_user_trace_setup *buts)
+                      struct block_device *bdev,
+                      struct blk_user_trace_setup *buts)
 {
        struct blk_trace *old_bt, *bt = NULL;
        struct dentry *dir = NULL;
        int ret, i;
+       struct hd_struct *part = NULL;
 
        if (!buts->buf_size || !buts->buf_nr)
                return -EINVAL;
@@ -411,11 +429,11 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
                if (buts->name[i] == '/')
                        buts->name[i] = '_';
 
-       ret = -ENOMEM;
        bt = kzalloc(sizeof(*bt), GFP_KERNEL);
        if (!bt)
-               goto err;
+               return -ENOMEM;
 
+       ret = -ENOMEM;
        bt->sequence = alloc_percpu(unsigned long);
        if (!bt->sequence)
                goto err;
@@ -426,11 +444,15 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
 
        ret = -ENOENT;
 
+       mutex_lock(&blk_tree_mutex);
        if (!blk_tree_root) {
                blk_tree_root = debugfs_create_dir("block", NULL);
-               if (!blk_tree_root)
+               if (!blk_tree_root) {
+                       mutex_unlock(&blk_tree_mutex);
                        goto err;
+               }
        }
+       mutex_unlock(&blk_tree_mutex);
 
        dir = debugfs_create_dir(buts->name, blk_tree_root);
 
@@ -460,11 +482,21 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
        if (!bt->act_mask)
                bt->act_mask = (u16) -1;
 
-       bt->start_lba = buts->start_lba;
-       bt->end_lba = buts->end_lba;
-       if (!bt->end_lba)
+       if (bdev)
+               part = bdev->bd_part;
+
+       if (part) {
+               bt->start_lba = part->start_sect;
+               bt->end_lba = part->start_sect + part->nr_sects;
+       } else
                bt->end_lba = -1ULL;
 
+       /* overwrite with user settings */
+       if (buts->start_lba)
+               bt->start_lba = buts->start_lba;
+       if (buts->end_lba)
+               bt->end_lba = buts->end_lba;
+
        bt->pid = buts->pid;
        bt->trace_state = Blktrace_setup;
 
@@ -475,26 +507,17 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
                goto err;
        }
 
-       if (atomic_add_return(1, &blk_probes_ref) == 1)
+       if (atomic_inc_return(&blk_probes_ref) == 1)
                blk_register_tracepoints();
 
        return 0;
 err:
-       if (bt) {
-               if (bt->msg_file)
-                       debugfs_remove(bt->msg_file);
-               if (bt->dropped_file)
-                       debugfs_remove(bt->dropped_file);
-               free_percpu(bt->sequence);
-               free_percpu(bt->msg_data);
-               if (bt->rchan)
-                       relay_close(bt->rchan);
-               kfree(bt);
-       }
+       blk_trace_free(bt);
        return ret;
 }
 
 int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
+                   struct block_device *bdev,
                    char __user *arg)
 {
        struct blk_user_trace_setup buts;
@@ -504,7 +527,7 @@ int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
        if (ret)
                return -EFAULT;
 
-       ret = do_blk_trace_setup(q, name, dev, &buts);
+       ret = do_blk_trace_setup(q, name, dev, bdev, &buts);
        if (ret)
                return ret;
 
@@ -572,7 +595,7 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
        switch (cmd) {
        case BLKTRACESETUP:
                bdevname(bdev, b);
-               ret = blk_trace_setup(q, b, bdev->bd_dev, arg);
+               ret = blk_trace_setup(q, b, bdev->bd_dev, bdev, arg);
                break;
        case BLKTRACESTART:
                start = 1;
@@ -633,7 +656,7 @@ static void blk_add_trace_rq(struct request_queue *q, struct request *rq,
        if (blk_pc_request(rq)) {
                what |= BLK_TC_ACT(BLK_TC_PC);
                __blk_add_trace(bt, 0, rq->data_len, rw, what, rq->errors,
-                               sizeof(rq->cmd), rq->cmd);
+                               rq->cmd_len, rq->cmd);
        } else  {
                what |= BLK_TC_ACT(BLK_TC_FS);
                __blk_add_trace(bt, rq->hard_sector, rq->hard_nr_sectors << 9,
@@ -924,6 +947,11 @@ static void fill_rwbs(char *rwbs, const struct blk_io_trace *t)
        int i = 0;
        int tc = t->action >> BLK_TC_SHIFT;
 
+       if (t->action == BLK_TN_MESSAGE) {
+               rwbs[i++] = 'N';
+               goto out;
+       }
+
        if (tc & BLK_TC_DISCARD)
                rwbs[i++] = 'D';
        else if (tc & BLK_TC_WRITE)
@@ -941,7 +969,7 @@ static void fill_rwbs(char *rwbs, const struct blk_io_trace *t)
                rwbs[i++] = 'S';
        if (tc & BLK_TC_META)
                rwbs[i++] = 'M';
-
+out:
        rwbs[i] = '\0';
 }
 
@@ -956,6 +984,16 @@ static inline const void *pdu_start(const struct trace_entry *ent)
        return te_blk_io_trace(ent) + 1;
 }
 
+static inline u32 t_action(const struct trace_entry *ent)
+{
+       return te_blk_io_trace(ent)->action;
+}
+
+static inline u32 t_bytes(const struct trace_entry *ent)
+{
+       return te_blk_io_trace(ent)->bytes;
+}
+
 static inline u32 t_sec(const struct trace_entry *ent)
 {
        return te_blk_io_trace(ent)->bytes >> 9;
@@ -988,51 +1026,115 @@ static void get_pdu_remap(const struct trace_entry *ent,
        r->sector = be64_to_cpu(sector);
 }
 
-static int blk_log_action_iter(struct trace_iterator *iter, const char *act)
+typedef int (blk_log_action_t) (struct trace_iterator *iter, const char *act);
+
+static int blk_log_action_classic(struct trace_iterator *iter, const char *act)
 {
        char rwbs[6];
-       unsigned long long ts  = ns2usecs(iter->ts);
-       unsigned long usec_rem = do_div(ts, USEC_PER_SEC);
+       unsigned long long ts  = iter->ts;
+       unsigned long nsec_rem = do_div(ts, NSEC_PER_SEC);
        unsigned secs          = (unsigned long)ts;
-       const struct trace_entry *ent = iter->ent;
-       const struct blk_io_trace *t = (const struct blk_io_trace *)ent;
+       const struct blk_io_trace *t = te_blk_io_trace(iter->ent);
 
        fill_rwbs(rwbs, t);
 
        return trace_seq_printf(&iter->seq,
-                               "%3d,%-3d %2d %5d.%06lu %5u %2s %3s ",
+                               "%3d,%-3d %2d %5d.%09lu %5u %2s %3s ",
                                MAJOR(t->device), MINOR(t->device), iter->cpu,
-                               secs, usec_rem, ent->pid, act, rwbs);
+                               secs, nsec_rem, iter->ent->pid, act, rwbs);
 }
 
-static int blk_log_action_seq(struct trace_seq *s, const struct blk_io_trace *t,
-                             const char *act)
+static int blk_log_action(struct trace_iterator *iter, const char *act)
 {
        char rwbs[6];
+       const struct blk_io_trace *t = te_blk_io_trace(iter->ent);
+
        fill_rwbs(rwbs, t);
-       return trace_seq_printf(s, "%3d,%-3d %2s %3s ",
+       return trace_seq_printf(&iter->seq, "%3d,%-3d %2s %3s ",
                                MAJOR(t->device), MINOR(t->device), act, rwbs);
 }
 
+static int blk_log_dump_pdu(struct trace_seq *s, const struct trace_entry *ent)
+{
+       const char *pdu_buf;
+       int pdu_len;
+       int i, end, ret;
+
+       pdu_buf = pdu_start(ent);
+       pdu_len = te_blk_io_trace(ent)->pdu_len;
+
+       if (!pdu_len)
+               return 1;
+
+       /* find the last zero that needs to be printed */
+       for (end = pdu_len - 1; end >= 0; end--)
+               if (pdu_buf[end])
+                       break;
+       end++;
+
+       if (!trace_seq_putc(s, '('))
+               return 0;
+
+       for (i = 0; i < pdu_len; i++) {
+
+               ret = trace_seq_printf(s, "%s%02x",
+                                      i == 0 ? "" : " ", pdu_buf[i]);
+               if (!ret)
+                       return ret;
+
+               /*
+                * stop when the rest is just zeroes and indicate so
+                * with a ".." appended
+                */
+               if (i == end && end != pdu_len - 1)
+                       return trace_seq_puts(s, " ..) ");
+       }
+
+       return trace_seq_puts(s, ") ");
+}
+
 static int blk_log_generic(struct trace_seq *s, const struct trace_entry *ent)
 {
        char cmd[TASK_COMM_LEN];
 
        trace_find_cmdline(ent->pid, cmd);
 
-       if (t_sec(ent))
-               return trace_seq_printf(s, "%llu + %u [%s]\n",
-                                       t_sector(ent), t_sec(ent), cmd);
-       return trace_seq_printf(s, "[%s]\n", cmd);
+       if (t_action(ent) & BLK_TC_ACT(BLK_TC_PC)) {
+               int ret;
+
+               ret = trace_seq_printf(s, "%u ", t_bytes(ent));
+               if (!ret)
+                       return 0;
+               ret = blk_log_dump_pdu(s, ent);
+               if (!ret)
+                       return 0;
+               return trace_seq_printf(s, "[%s]\n", cmd);
+       } else {
+               if (t_sec(ent))
+                       return trace_seq_printf(s, "%llu + %u [%s]\n",
+                                               t_sector(ent), t_sec(ent), cmd);
+               return trace_seq_printf(s, "[%s]\n", cmd);
+       }
 }
 
 static int blk_log_with_error(struct trace_seq *s,
                              const struct trace_entry *ent)
 {
-       if (t_sec(ent))
-               return trace_seq_printf(s, "%llu + %u [%d]\n", t_sector(ent),
-                                       t_sec(ent), t_error(ent));
-       return trace_seq_printf(s, "%llu [%d]\n", t_sector(ent), t_error(ent));
+       if (t_action(ent) & BLK_TC_ACT(BLK_TC_PC)) {
+               int ret;
+
+               ret = blk_log_dump_pdu(s, ent);
+               if (ret)
+                       return trace_seq_printf(s, "[%d]\n", t_error(ent));
+               return 0;
+       } else {
+               if (t_sec(ent))
+                       return trace_seq_printf(s, "%llu + %u [%d]\n",
+                                               t_sector(ent),
+                                               t_sec(ent), t_error(ent));
+               return trace_seq_printf(s, "%llu [%d]\n",
+                                       t_sector(ent), t_error(ent));
+       }
 }
 
 static int blk_log_remap(struct trace_seq *s, const struct trace_entry *ent)
@@ -1074,6 +1176,17 @@ static int blk_log_split(struct trace_seq *s, const struct trace_entry *ent)
                                get_pdu_int(ent), cmd);
 }
 
+static int blk_log_msg(struct trace_seq *s, const struct trace_entry *ent)
+{
+       int ret;
+       const struct blk_io_trace *t = te_blk_io_trace(ent);
+
+       ret = trace_seq_putmem(s, t + 1, t->pdu_len);
+       if (ret)
+               return trace_seq_putc(s, '\n');
+       return ret;
+}
+
 /*
  * struct tracer operations
  */
@@ -1088,8 +1201,7 @@ static void blk_tracer_print_header(struct seq_file *m)
 
 static void blk_tracer_start(struct trace_array *tr)
 {
-       if (atomic_add_return(1, &blk_probes_ref) == 1)
-               blk_register_tracepoints();
+       blk_tracer_enabled = true;
        trace_flags &= ~TRACE_ITER_CONTEXT_INFO;
 }
 
@@ -1097,23 +1209,17 @@ static int blk_tracer_init(struct trace_array *tr)
 {
        blk_tr = tr;
        blk_tracer_start(tr);
-       blk_tracer_enabled = true;
        return 0;
 }
 
 static void blk_tracer_stop(struct trace_array *tr)
 {
+       blk_tracer_enabled = false;
        trace_flags |= TRACE_ITER_CONTEXT_INFO;
-       if (atomic_dec_and_test(&blk_probes_ref))
-               blk_unregister_tracepoints();
 }
 
 static void blk_tracer_reset(struct trace_array *tr)
 {
-       if (!atomic_read(&blk_probes_ref))
-               return;
-
-       blk_tracer_enabled = false;
        blk_tracer_stop(tr);
 }
 
@@ -1138,29 +1244,48 @@ static const struct {
        [__BLK_TA_REMAP]        = {{  "A", "remap" },      blk_log_remap },
 };
 
-static enum print_line_t blk_trace_event_print(struct trace_iterator *iter,
-                                              int flags)
+static enum print_line_t print_one_line(struct trace_iterator *iter,
+                                       bool classic)
 {
        struct trace_seq *s = &iter->seq;
-       const struct blk_io_trace *t = (struct blk_io_trace *)iter->ent;
-       const u16 what = t->action & ((1 << BLK_TC_SHIFT) - 1);
+       const struct blk_io_trace *t;
+       u16 what;
        int ret;
+       bool long_act;
+       blk_log_action_t *log_action;
 
-       if (!trace_print_context(iter))
-               return TRACE_TYPE_PARTIAL_LINE;
+       t          = te_blk_io_trace(iter->ent);
+       what       = t->action & ((1 << BLK_TC_SHIFT) - 1);
+       long_act   = !!(trace_flags & TRACE_ITER_VERBOSE);
+       log_action = classic ? &blk_log_action_classic : &blk_log_action;
 
-       if (unlikely(what == 0 || what > ARRAY_SIZE(what2act)))
-               ret = trace_seq_printf(s, "Bad pc action %x\n", what);
+       if (t->action == BLK_TN_MESSAGE) {
+               ret = log_action(iter, long_act ? "message" : "m");
+               if (ret)
+                       ret = blk_log_msg(s, iter->ent);
+               goto out;
+       }
+
+       if (unlikely(what == 0 || what >= ARRAY_SIZE(what2act)))
+               ret = trace_seq_printf(s, "Unknown action %x\n", what);
        else {
-               const bool long_act = !!(trace_flags & TRACE_ITER_VERBOSE);
-               ret = blk_log_action_seq(s, t, what2act[what].act[long_act]);
+               ret = log_action(iter, what2act[what].act[long_act]);
                if (ret)
                        ret = what2act[what].print(s, iter->ent);
        }
-
+out:
        return ret ? TRACE_TYPE_HANDLED : TRACE_TYPE_PARTIAL_LINE;
 }
 
+static enum print_line_t blk_trace_event_print(struct trace_iterator *iter,
+                                              int flags)
+{
+       if (!trace_print_context(iter))
+               return TRACE_TYPE_PARTIAL_LINE;
+
+       return print_one_line(iter, false);
+}
+
 static int blk_trace_synthesize_old_trace(struct trace_iterator *iter)
 {
        struct trace_seq *s = &iter->seq;
@@ -1168,7 +1293,7 @@ static int blk_trace_synthesize_old_trace(struct trace_iterator *iter)
        const int offset = offsetof(struct blk_io_trace, sector);
        struct blk_io_trace old = {
                .magic    = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION,
-               .time     = ns2usecs(iter->ts),
+               .time     = iter->ts,
        };
 
        if (!trace_seq_putmem(s, &old, offset))
@@ -1186,26 +1311,10 @@ blk_trace_event_print_binary(struct trace_iterator *iter, int flags)
 
 static enum print_line_t blk_tracer_print_line(struct trace_iterator *iter)
 {
-       const struct blk_io_trace *t;
-       u16 what;
-       int ret;
-
        if (!(blk_tracer_flags.val & TRACE_BLK_OPT_CLASSIC))
                return TRACE_TYPE_UNHANDLED;
 
-       t = (const struct blk_io_trace *)iter->ent;
-       what = t->action & ((1 << BLK_TC_SHIFT) - 1);
-
-       if (unlikely(what == 0 || what > ARRAY_SIZE(what2act)))
-               ret = trace_seq_printf(&iter->seq, "Bad pc action %x\n", what);
-       else {
-               const bool long_act = !!(trace_flags & TRACE_ITER_VERBOSE);
-               ret = blk_log_action_iter(iter, what2act[what].act[long_act]);
-               if (ret)
-                       ret = what2act[what].print(&iter->seq, iter->ent);
-       }
-
-       return ret ? TRACE_TYPE_HANDLED : TRACE_TYPE_PARTIAL_LINE;
+       return print_one_line(iter, true);
 }
 
 static struct tracer blk_tracer __read_mostly = {
@@ -1251,7 +1360,10 @@ static int blk_trace_remove_queue(struct request_queue *q)
        if (bt == NULL)
                return -EINVAL;
 
-       kfree(bt);
+       if (atomic_dec_and_test(&blk_probes_ref))
+               blk_unregister_tracepoints();
+
+       blk_trace_free(bt);
        return 0;
 }
 
@@ -1261,24 +1373,34 @@ static int blk_trace_remove_queue(struct request_queue *q)
 static int blk_trace_setup_queue(struct request_queue *q, dev_t dev)
 {
        struct blk_trace *old_bt, *bt = NULL;
+       int ret = -ENOMEM;
 
        bt = kzalloc(sizeof(*bt), GFP_KERNEL);
        if (!bt)
                return -ENOMEM;
 
+       bt->msg_data = __alloc_percpu(BLK_TN_MAX_MSG, __alignof__(char));
+       if (!bt->msg_data)
+               goto free_bt;
+
        bt->dev = dev;
        bt->act_mask = (u16)-1;
        bt->end_lba = -1ULL;
-       bt->trace_state = Blktrace_running;
 
        old_bt = xchg(&q->blk_trace, bt);
        if (old_bt != NULL) {
                (void)xchg(&q->blk_trace, old_bt);
-               kfree(bt);
-               return -EBUSY;
+               ret = -EBUSY;
+               goto free_bt;
        }
 
+       if (atomic_inc_return(&blk_probes_ref) == 1)
+               blk_register_tracepoints();
        return 0;
+
+free_bt:
+       blk_trace_free(bt);
+       return ret;
 }
 
 /*
@@ -1340,12 +1462,12 @@ static int blk_trace_str2mask(const char *str)
 {
        int i;
        int mask = 0;
-       char *s, *token;
+       char *buf, *s, *token;
 
-       s = kstrdup(str, GFP_KERNEL);
-       if (s == NULL)
+       buf = kstrdup(str, GFP_KERNEL);
+       if (buf == NULL)
                return -ENOMEM;
-       s = strstrip(s);
+       s = strstrip(buf);
 
        while (1) {
                token = strsep(&s, ",");
@@ -1366,7 +1488,7 @@ static int blk_trace_str2mask(const char *str)
                        break;
                }
        }
-       kfree(s);
+       kfree(buf);
 
        return mask;
 }