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powerpc/powernv: Fix sysparam sysfs error handling

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When a sysparam query in OPAL returned a negative value (error code),
sysfs would spew out a decent chunk of memory; almost 64K more than
expected. This was traced to a sign/unsigned mix up in the OPAL sysparam
sysfs code at sys_param_show.

The return value of sys_param_show is a ssize_t, calculated using

  return ret ? ret : attr->param_size;

Alan Modra explains:

  "attr->param_size" is an unsigned int, "ret" an int, so the overall
  expression has type unsigned int.  Result is that ret is cast to
  unsigned int before being cast to ssize_t.

Instead of using the ternary operator, set ret to the param_size if an
error is not detected. The same bug exists in the sysfs write callback;
this patch fixes it in the same way.

A note on debugging this next time: on my system gcc will warn about
this if compiled with -Wsign-compare, which is not enabled by -Wall,
only -Wextra.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Joel Stanley 2014-04-24 16:55:33 +09:30 committed by Benjamin Herrenschmidt
parent 4fb8d027dc
commit ba9a32b176
1 changed files with 5 additions and 2 deletions
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7
arch/powerpc/platforms/powernv/opal-sysparam.c
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@ -121,9 +121,10 @@ static ssize_t sys_param_show(struct kobject *kobj,
memcpy(buf, param_data_buf, attr->param_size); memcpy(buf, param_data_buf, attr->param_size);
ret = attr->param_size;
out: out:
mutex_unlock(&opal_sysparam_mutex); mutex_unlock(&opal_sysparam_mutex);
return ret ? ret : attr->param_size; return ret;
} }
static ssize_t sys_param_store(struct kobject *kobj, static ssize_t sys_param_store(struct kobject *kobj,
@ -138,7 +139,9 @@ static ssize_t sys_param_store(struct kobject *kobj,
ret = opal_set_sys_param(attr->param_id, attr->param_size, ret = opal_set_sys_param(attr->param_id, attr->param_size,
param_data_buf); param_data_buf);
mutex_unlock(&opal_sysparam_mutex); mutex_unlock(&opal_sysparam_mutex);
return ret ? ret : count; if (!ret)
ret = count;
return ret;
} }
void __init opal_sys_param_init(void) void __init opal_sys_param_init(void)