Messages in this thread | | | From | Schspa Shi <> | Date | Fri, 13 May 2022 00:01:16 +0800 | Subject | Re: [PATCH v4 2/2] cpufreq: make interface functions and lock holding state clear |
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"Rafael J. Wysocki" <rafael@kernel.org> writes:
> On Thu, May 12, 2022 at 3:52 PM Schspa Shi <schspa@gmail.com> wrote: >> >> cpufreq_offline() calls offline() and exit() under the policy rwsem >> But they are called outside the rwsem in cpufreq_online(). >> >> This patch move the offline(), exit(), online(), init() to be inside >> of policy rwsem to achieve a clear lock relationship. >> >> All the init() online() implement only initialize policy object without >> holding this lock and won't call cpufreq APIs need to hold this lock. >> >> Signed-off-by: Schspa Shi <schspa@gmail.com> > > IMV this still addresses 2 different issues and so it should be split > into 2 different patches. > >> --- >> drivers/cpufreq/cpufreq.c | 5 ++--- >> 1 file changed, 2 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c >> index 35dffd738580..f242d5488364 100644 >> --- a/drivers/cpufreq/cpufreq.c >> +++ b/drivers/cpufreq/cpufreq.c > > Patch 1: > >> @@ -1343,12 +1343,12 @@ static int cpufreq_online(unsigned int cpu) >> down_write(&policy->rwsem); >> policy->cpu = cpu; >> policy->governor = NULL; >> - up_write(&policy->rwsem); >> } else { >> new_policy = true; >> policy = cpufreq_policy_alloc(cpu); >> if (!policy) >> return -ENOMEM; >> + down_write(&policy->rwsem); >> } >> >> if (!new_policy && cpufreq_driver->online) { >> @@ -1388,7 +1388,6 @@ static int cpufreq_online(unsigned int cpu) >> cpumask_copy(policy->related_cpus, policy->cpus); >> } >> >> - down_write(&policy->rwsem); >> /* >> * affected cpus must always be the one, which are online. We aren't >> * managing offline cpus here. > > which addresses the problem that cpufreq_online() updates the > policy->cpus and related_cpus masks without holding the policy rwsem > (since the policy kobject has been registered already at this point, > this is generally unsafe). > > A side-effect of it is that ->online() and ->init() will be called > under the policy rwsem now, but that should be fine and is more > consistent than the current code too. > > Patch 2: > >> @@ -1540,7 +1539,6 @@ static int cpufreq_online(unsigned int cpu) >> remove_cpu_dev_symlink(policy, get_cpu_device(j)); >> >> cpumask_clear(policy->cpus); >> - up_write(&policy->rwsem); >> >> out_offline_policy: >> if (cpufreq_driver->offline) >> @@ -1549,6 +1547,7 @@ static int cpufreq_online(unsigned int cpu) >> out_exit_policy: >> if (cpufreq_driver->exit) >> cpufreq_driver->exit(policy); >> + up_write(&policy->rwsem); >> >> out_free_policy: >> cpufreq_policy_free(policy); >> -- > > which addressed the issue of calling ->offline() and ->exit() without > holding the policy rwsem that is at best inconsistent with > cpufreq_offline().
No, we can't split this into two different patches. which will cause a uninitialized unlock for policy rwsem. This will make the git bitsec unusable.
Which Dan Carpenter reported, and cause the patch of the v1 version to be reverted.
Link: https://lore.kernel.org/all/YnKZCGaig+EXSowf@kili/
--- BRs
Schspa Shi
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