hw-breakpoints: Get the number of available registers on boot dynamically

The breakpoint generic layer assumes that archs always know in advance
the static number of address registers available to host breakpoints
through the HBP_NUM macro.

However this is not true for every archs. For example Arm needs to get
this information dynamically to handle the compatiblity between
different versions.

To solve this, this patch proposes to drop the static HBP_NUM macro
and let the arch provide the number of available slots through a
new hw_breakpoint_slots() function. For archs that have
CONFIG_HAVE_MIXED_BREAKPOINTS_REGS selected, it will be called once
as the number of registers fits for instruction and data breakpoints
together.
For the others it will be called first to get the number of
instruction breakpoint registers and another time to get the
data breakpoint registers, the targeted type is given as a
parameter of hw_breakpoint_slots().

Reported-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Cc: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Cc: K. Prasad <prasad@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 19 deletions

diff --git a/kernel/trace/trace_ksym.c b/kernel/trace/trace_ksym.c
index d59cd6879477..8eaf00749b65 100644
--- a/kernel/trace/trace_ksym.c
+++ b/kernel/trace/trace_ksym.c
@@ -34,12 +34,6 @@
 
 #include <asm/atomic.h>
 
-/*
- * For now, let us restrict the no. of symbols traced simultaneously to number
- * of available hardware breakpoint registers.
- */
-#define KSYM_TRACER_MAX HBP_NUM
-
 #define KSYM_TRACER_OP_LEN 3 /* rw- */
 
 struct trace_ksym {
@@ -53,7 +47,6 @@ struct trace_ksym {
 
 static struct trace_array *ksym_trace_array;
 
-static unsigned int ksym_filter_entry_count;
 static unsigned int ksym_tracing_enabled;
 
 static HLIST_HEAD(ksym_filter_head);
@@ -181,13 +174,6 @@ int process_new_ksym_entry(char *ksymname, int op, unsigned long addr)
         struct trace_ksym *entry;
         int ret = -ENOMEM;
 
-        if (ksym_filter_entry_count >= KSYM_TRACER_MAX) {
-                printk(KERN_ERR "ksym_tracer: Maximum limit:(%d) reached. No"
-                " new requests for tracing can be accepted now.\n",
-                        KSYM_TRACER_MAX);
-                return -ENOSPC;
-        }
-
         entry = kzalloc(sizeof(struct trace_ksym), GFP_KERNEL);
         if (!entry)
                 return -ENOMEM;
@@ -203,13 +189,17 @@ int process_new_ksym_entry(char *ksymname, int op, unsigned long addr)
 
         if (IS_ERR(entry->ksym_hbp)) {
                 ret = PTR_ERR(entry->ksym_hbp);
-                printk(KERN_INFO "ksym_tracer request failed. Try again"
-                                        " later!!\n");
+                if (ret == -ENOSPC) {
+                        printk(KERN_ERR "ksym_tracer: Maximum limit reached."
+                        " No new requests for tracing can be accepted now.\n");
+                } else {
+                        printk(KERN_INFO "ksym_tracer request failed. Try again"
+                                         " later!!\n");
+                }
                 goto err;
         }
 
         hlist_add_head_rcu(&(entry->ksym_hlist), &ksym_filter_head);
-        ksym_filter_entry_count++;
 
         return 0;
 
@@ -265,7 +255,6 @@ static void __ksym_trace_reset(void)
         hlist_for_each_entry_safe(entry, node, node1, &ksym_filter_head,
                                                                 ksym_hlist) {
                 unregister_wide_hw_breakpoint(entry->ksym_hbp);
-                ksym_filter_entry_count--;
                 hlist_del_rcu(&(entry->ksym_hlist));
                 synchronize_rcu();
                 kfree(entry);
@@ -338,7 +327,6 @@ static ssize_t ksym_trace_filter_write(struct file *file,
                                 goto out_unlock;
                 }
                 /* Error or "symbol:---" case: drop it */
-                ksym_filter_entry_count--;
                 hlist_del_rcu(&(entry->ksym_hlist));
                 synchronize_rcu();
                 kfree(entry);