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SubjectRe: [PATCH] clk: fix a panic error caused by accessing NULL pointer
On 11/21, Chunyan Zhang wrote:
> On 21 November 2017 at 16:57, Chunyan Zhang <zhang.lyra@gmail.com> wrote:
> > On 21 November 2017 at 03:12, Stephen Boyd <sboyd@codeaurora.org> wrote:
> >> On 11/20, Chunyan Zhang wrote:
> >>> From: Cai Li <cai.li@spreadtrum.com>
> >>>
> >>> In some cases the clock parent would be set NULL when doing re-parent,
> >>> it will cause a NULL pointer accessing if clk_set trace event is enabled,
> >>> since the trace event function would not check the input parameter.
> >>>
> >>> Signed-off-by: Cai Li <cai.li@spreadtrum.com>
> >>> Signed-off-by: Chunyan Zhang <chunyan.zhang@spreadtrum.com>
> >>
> >> Fixes: tag?
> >>
> >>> ---
> >>> drivers/clk/clk.c | 9 ++++-----
> >>> 1 file changed, 4 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> >>> index c8d83ac..64efaf0 100644
> >>> --- a/drivers/clk/clk.c
> >>> +++ b/drivers/clk/clk.c
> >>> @@ -1242,13 +1242,12 @@ static int __clk_set_parent(struct clk_core *core, struct clk_core *parent,
> >>>
> >>> old_parent = __clk_set_parent_before(core, parent);
> >>>
> >>> - trace_clk_set_parent(core, parent);
> >>> -
> >>> /* change clock input source */
> >>> - if (parent && core->ops->set_parent)
> >>> + if (parent && core->ops->set_parent) {
> >>> + trace_clk_set_parent(core, parent);
> >>> ret = core->ops->set_parent(core->hw, p_index);
> >>> -
> >>> - trace_clk_set_parent_complete(core, parent);
> >>> + trace_clk_set_parent_complete(core, parent);
> >>> + }
> >>
> >> Is the problem that parent may be NULL and the tracepoint
> >> dereferences it?
> >
> > Yes, I think that probably is uncommon usage though, it revealed that
> > the tracepoint could be stronger :)
>
> The reason we need to set the parent as NULL is to disable the clk for
> the purpose of saving power.

Do you have drivers calling set_parent with NULL to save power?
Seems sort of odd. Why not do something when disabling the clk in
clk_disable() path instead? Either way, I'll apply the patch to
clk-fixes.

--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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