On Tue, Oct 21, 2025 at 11:56:30AM -1000, Tejun Heo wrote: > Hello, > > On Tue, Oct 21, 2025 at 02:39:50PM -0700, Matthew Brost wrote: > > Drivers often use workqueues that are in the reclaim path (e.g., DRM > > scheduler workqueues). It is useful to teach lockdep that memory cannot > > be allocated on these workqueues. Add an interface to taint workqueue > > lockdep with reclaim. > > Given that it's about reclaim, "memory cannot be allocated" may be a bit > misleading. Can you make the description more accurate? Also, it'd be great > if you can include an example lockdep splat for reference. > > > Cc: Tejun Heo <[email protected]> > > Cc: Lai Jiangshan <[email protected]> > > Signed-off-by: Matthew Brost <[email protected]> > > --- > > include/linux/workqueue.h | 19 +++++++++++++++++++ > > kernel/workqueue.c | 9 +++++++++ > > 2 files changed, 28 insertions(+) > > > > diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h > > index dabc351cc127..954c7eb7e225 100644 > > --- a/include/linux/workqueue.h > > +++ b/include/linux/workqueue.h > > @@ -553,6 +553,25 @@ alloc_workqueue_lockdep_map(const char *fmt, unsigned > > int flags, int max_active, > > 1, lockdep_map, ##args)) > > #endif > > > > + > > +#ifdef CONFIG_LOCKDEP > > +/** > > + * taint_reclaim_workqueue - taint workqueue lockdep map with reclaim > > + * @wq: workqueue to taint with reclaim > > + * gfp: gfp taint > ^@ > > > + * > > + * Drivers often use workqueues that are in the reclaim path (e.g., DRM > > + * scheduler workqueues). It is useful to teach lockdep that memory cannot > > be > > + * allocated on these workqueues. > > + */ > > +extern void taint_reclaim_workqueue(struct workqueue_struct *wq, gfp_t > > gfp); > > +#else > > +static inline void taint_reclaim_workqueue(struct workqueue_struct *wq, > > + gfp_t gfp) > > Would a more direct name work better, maybe something like > workqueue_warn_on_reclaim()? >
Can rename, but perhaps not needed depending on what we land on below. > Hmm... would it make sense to tie this to WQ_MEM_RECLAIM - ie. enable it > implicitly on workqueues w/ the flag set? > I had considered this, and for a while I thought WQ_MEM_RECLAIM already did what I'm suggesting—especially since I’ve spotted bugs in drivers where I would have expected lockdep to catch them. In my opinion, this approach is better, but it has a broader kernel-wide scope and could potentially break some things. My subsequent patches will likely break one or two DRM drivers, so it might not be a concern to fix everything that breaks across the kernel. It's up to you which route we want to take here. Matt > Thanks. > > -- > tejun
