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Subject[PATCH] tracing: use kstrdup_const instead of private implementation
Date
The kernel now has kstrdup_const/kfree_const for reusing .rodata
(typically string literals) when possible; there's no reason to
duplicate that logic in the tracing system. Moreover, as the comment
above core_kernel_data states, it may not always return true for
.rodata - that is for example the case on x86_64, where we thus end up
kstrdup'ing all the passed-in strings.

Arguably, testing for .rodata explicitly (as kstrdup_const does) is
also more correct: I don't think one is supposed to be able to change
the name after creating the event_subsystem by passing the address of
a static char (but non-const) array.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
kernel/trace/trace_events.c | 24 ++++++++----------------
1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 7ca09cdc20c2..ae97d73b31fa 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -38,21 +38,19 @@ static LIST_HEAD(ftrace_common_fields);
static struct kmem_cache *field_cachep;
static struct kmem_cache *file_cachep;

-#define SYSTEM_FL_FREE_NAME (1 << 31)
-
static inline int system_refcount(struct event_subsystem *system)
{
- return system->ref_count & ~SYSTEM_FL_FREE_NAME;
+ return system->ref_count;
}

static int system_refcount_inc(struct event_subsystem *system)
{
- return (system->ref_count++) & ~SYSTEM_FL_FREE_NAME;
+ return system->ref_count++;
}

static int system_refcount_dec(struct event_subsystem *system)
{
- return (--system->ref_count) & ~SYSTEM_FL_FREE_NAME;
+ return --system->ref_count;
}

/* Double loops, do not use break, only goto's work */
@@ -460,8 +458,7 @@ static void __put_system(struct event_subsystem *system)
kfree(filter->filter_string);
kfree(filter);
}
- if (system->ref_count & SYSTEM_FL_FREE_NAME)
- kfree(system->name);
+ kfree_const(system->name);
kfree(system);
}

@@ -1492,13 +1489,9 @@ create_new_subsystem(const char *name)
system->ref_count = 1;

/* Only allocate if dynamic (kprobes and modules) */
- if (!core_kernel_data((unsigned long)name)) {
- system->ref_count |= SYSTEM_FL_FREE_NAME;
- system->name = kstrdup(name, GFP_KERNEL);
- if (!system->name)
- goto out_free;
- } else
- system->name = name;
+ system->name = kstrdup_const(name, GFP_KERNEL);
+ if (!system->name)
+ goto out_free;

system->filter = NULL;

@@ -1511,8 +1504,7 @@ create_new_subsystem(const char *name)
return system;

out_free:
- if (system->ref_count & SYSTEM_FL_FREE_NAME)
- kfree(system->name);
+ kfree_const(system->name);
kfree(system);
return NULL;
}
--
2.1.3


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