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tracing: Free histogram var refs regardless of how often they are referenced

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Using the same variable three or more times in one hist trigger leaks the
variable reference and its strings when the trigger is removed.

commit 656fe2ba85 ("tracing: Use hist trigger's var_ref array to destroy
var_refs") made a trigger's var_refs[] array the only owner of a var ref:
destroy_hist_field() returns early for HIST_FIELD_FL_VAR_REF, so the field
expressions never destroy one. One entry, freed once, no count needed.

commit 8bcebc77e8 ("tracing: Fix histogram code when expression has same
var as value") then made repeated references share one object and added a
count of them. Only the increment side exists, since those expressions
still return early and never drop a reference, so __destroy_hist_field()
sees how many references were created rather than how many are left. It
frees when the decremented count is 0 or 1, so two references work and
three or more leak.

Sharing kept one array entry per object, and create_var_ref() searches and
appends within a single trigger, so nothing outside it holds the object.
Removing a trigger whose variables are still referenced is already refused
by check_var_refs() with -EBUSY. Drop the count and free unconditionally.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260906124025.3550596-1-donggeunyoo.kernel@gmail.com
Fixes: 8bcebc77e8 ("tracing: Fix histogram code when expression has same var as value")
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Donggeun Yoo 2026-09-06 21:40:25 +09:00 committed by Steven Rostedt
parent 0701995aaf
commit 4bddcb346a
1 changed files with 1 additions and 15 deletions
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16
kernel/trace/trace_events_hist.c
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@ -169,7 +169,6 @@ struct hist_field {
struct hist_field *operands[HIST_FIELD_OPERANDS_MAX];
struct hist_trigger_data *hist_data;
enum hist_field_fn fn_num;
unsigned int ref;
unsigned int size;
unsigned int offset;
unsigned int is_signed;
@ -1913,16 +1912,8 @@ static int contains_operator(char *str, char **sep)
return field_op;
}
static void get_hist_field(struct hist_field *hist_field)
{
hist_field->ref++;
}
static void __destroy_hist_field(struct hist_field *hist_field)
{
if (--hist_field->ref > 1)
return;
kfree(hist_field->var.name);
kfree(hist_field->name);
@ -1969,8 +1960,6 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
if (!hist_field)
return NULL;
hist_field->ref = 1;
hist_field->hist_data = hist_data;
if (flags & HIST_FIELD_FL_EXPR || flags & HIST_FIELD_FL_ALIAS)
@ -2223,10 +2212,8 @@ static struct hist_field *create_var_ref(struct hist_trigger_data *hist_data,
for (i = 0; i < hist_data->n_var_refs; i++) {
ref_field = hist_data->var_refs[i];
if (ref_field->var.idx == var_field->var.idx &&
ref_field->var.hist_data == var_field->hist_data) {
get_hist_field(ref_field);
ref_field->var.hist_data == var_field->hist_data)
return ref_field;
}
}
/* Sanity check to avoid out-of-bound write on 'hist_data->var_refs' */
if (hist_data->n_var_refs >= TRACING_MAP_VARS_MAX)
@ -3276,7 +3263,6 @@ static struct hist_field *create_var(struct hist_trigger_data *hist_data,
goto out;
}
var->ref = 1;
var->flags = HIST_FIELD_FL_VAR;
var->var.idx = idx;
var->var.hist_data = var->hist_data = hist_data;