Quoting Martin Blumenstingl (2019-08-15 15:31:55) > Don't compare the parent clock name with a NULL name in the > clk_parent_map. This prevents a kernel crash when passing NULL > core->parents[i].name to strcmp(). > > An example which triggered this is a mux clock with four parents when > each of them is referenced in the clock driver using > clk_parent_data.fw_name and then calling clk_set_parent(clk, 3rd_parent) > on this mux. > In this case the first parent is also the HW default so > core->parents[i].hw is populated when the clock is registered. Calling > clk_set_parent(clk, 3rd_parent) will then go through all parents and > skip the first parent because it's hw pointer doesn't match. For the > second parent no hw pointer is cached yet and clk_core_get(core, 1) > returns a non-matching pointer (which is correct because we are comparing > the second with the third parent). Comparing the result of > clk_core_get(core, 2) with the requested parent gives a match. However > we don't reach this point because right after the clk_core_get(core, 1) > mismatch the old code tried to !strcmp(parent->name, NULL) (where the > second argument is actually core->parents[i].name, but that was never > populated by the clock driver). > > Signed-off-by: Martin Blumenstingl <[email protected]> > --- > I have seen the original crash when I was testing an MMC driver which > is not upstream yet on v5.3-rc4. I'm not sure whether this fix is > "correct" (it fixes the crash for me) or where to point the Fixes tag > to, it may be one of: > - fc0c209c147f ("clk: Allow parents to be specified without string names") > - 1a079560b145 ("clk: Cache core in clk_fetch_parent_index() without names") > > This is meant to be applied on top of v5.3-rc4. >
Ah ok. I thought that strcmp() would ignore NULL arguments, but apparently not. I can apply this to clk-fixes.
