[PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules
Paul E. McKenney
paulmck at linux.ibm.com
Tue Apr 2 15:23:34 UTC 2019
On Tue, Apr 02, 2019 at 11:14:40AM -0400, Mathieu Desnoyers wrote:
> ----- On Apr 2, 2019, at 10:28 AM, paulmck paulmck at linux.ibm.com wrote:
>
> > Hello!
> >
> > This series prohibits use of DEFINE_SRCU() and DEFINE_STATIC_SRCU()
> > by loadable modules. The reason for this prohibition is the fact
> > that using these two macros within modules requires that the size of
> > the reserved region be increased, which is not something we want to
> > be doing all that often. Instead, loadable modules should define an
> > srcu_struct and invoke init_srcu_struct() from their module_init function
> > and cleanup_srcu_struct() from their module_exit function. Note that
> > modules using call_srcu() will also need to invoke srcu_barrier() from
> > their module_exit function.
>
> This arbitrary API limitation seems weird.
>
> Isn't there a way to allow modules to use DEFINE_SRCU and DEFINE_STATIC_SRCU
> while implementing them with dynamic allocation under the hood ?
Although call_srcu() already has initialization hooks, some would
also be required in srcu_read_lock(), and I am concerned about adding
memory allocation at that point, especially given the possibility
of memory-allocation failure. And the possibility that the first
srcu_read_lock() happens in an interrupt handler or similar.
Or am I missing a trick here?
Thanx, Paul
> Thanks,
>
> Mathieu
>
>
> >
> > This series consist of the following:
> >
> > 1. Dynamically allocate dax_srcu.
> >
> > 2. Dynamically allocate drm_unplug_srcu.
> >
> > 3. Dynamically allocate kfd_processes_srcu.
> >
> > These build and have been subjected to 0day testing, but might also need
> > testing by someone having the requisite hardware.
> >
> > Thanx, Paul
> >
> > ------------------------------------------------------------------------
> >
> > drivers/dax/super.c | 10 +++++-
> > drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c | 5 +++
> > drivers/gpu/drm/amd/amdkfd/kfd_process.c | 2 -
> > drivers/gpu/drm/drm_drv.c | 8 ++++
> > include/linux/srcutree.h | 19 +++++++++--
> > kernel/rcu/rcuperf.c | 40 +++++++++++++++++++-----
> > kernel/rcu/rcutorture.c | 48 +++++++++++++++++++++--------
> > 7 files changed, 105 insertions(+), 27 deletions(-)
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
>
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