On 7/21/26 10:09 PM, Vlastimil Babka (SUSE) wrote: > On 7/20/26 14:44, Harry Yoo (Oracle) wrote: >> Currently, k[v]free_rcu() cannot be called in unknown context since >> it could lead to a deadlock when called in the middle of k[v]free_rcu(). >> >> Make users' lives easier by introducing kfree_rcu_nolock() variant, >> now that kfree_rcu_sheaf() is available on PREEMPT_RT and >> __kfree_rcu_sheaf() handles unknown context. >> >> kfree_rcu_nolock() falls back to the kvfree_rcu batching when sheaves >> path fails. > > From the code I would say it falls back to defer_kfree_rcu(), which is an > irq_work that does kvfree_rcu batching?
Indeed that was what I intended to say, but I messed up while writing it :-) Will fix that. > Otherwise the sentence would contradict the following: > >> In most cases, the sheaves path is expected to succeed >> and it's unnecessary to add complexity to the existing kvfree_rcu >> batching by teaching it how to handle unknown context. > > This talks about trying to perform the batching immediately without defering. You mean the earlier sentence "kfree_rcu_nolock() falls back to the kvfree_rcu batching when sheaves path fails", right? >> Since defer_kfree_rcu() can be called on caches without sheaves, move >> deferred_work_barrier() and rcu_barrier() outside the branch in >> kvfree_rcu_barrier_on_cache(). >> >> Signed-off-by: Harry Yoo (Oracle) <[email protected]> > > Other than that and a comment correction below, LGTM. > > Reviewed-by: Vlastimil Babka (SUSE) <[email protected]> Thanks! >> --- >> include/linux/rcupdate.h | 19 +++++++++++++++++++ >> mm/slab_common.c | 28 ++++++++++++++++++++++++++-- >> mm/slub.c | 24 +++++++++++++++++++++++- >> 3 files changed, 68 insertions(+), 3 deletions(-) >> >> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h >> index ef5bb6981133..ce0fd401352e 100644 >> --- a/include/linux/rcupdate.h >> +++ b/include/linux/rcupdate.h >> @@ -1099,6 +1099,7 @@ static inline void rcu_read_unlock_migrate(void) >> * In mm/slab_common.c, no suitable header to include here. >> */ >> void kvfree_call_rcu(struct kvfree_rcu_head *head, void *ptr); >> +void kfree_call_rcu_nolock(struct kvfree_rcu_head *head, void *ptr); >> >> /* >> * The BUILD_BUG_ON() makes sure the rcu_head offset can be handled. See the >> @@ -1124,6 +1125,24 @@ do { >> \ >> kvfree_call_rcu(NULL, (void *) (___p)); \ >> } while (0) >> >> +/** >> + * kfree_rcu_nolock() - a version of kfree_rcu() that can be called in any >> context. >> + * @ptr: pointer to kfree for double-argument invocations. >> + * @kvrhf: the name of the struct kvfree_rcu_head within the type of @ptr. >> + * >> + * Objects that are not allocated via kmalloc_nolock() are not supported. > > Is this true? If __kfree_rcu_sheaf() succeeds, rcu_sheaf is either flushed > normally (call_rcu with rcu_free_sheaf()) or via the irq_work doing the > same. The defer_kfree_rcu() fallback ends up doing a normal > kvfree_call_rcu(). I don't see any path that ends up doing kfree_nolock(). > Am I missing something? I added this limitation because I thought it doesn't make sense to support this when we don't support large kmalloc and vmalloc in unknown context. Perhaps too limiting than it should be though. >> + * kfree_rcu_nolock() supports 2-arg variant only. >> + */ >> +#define kfree_rcu_nolock(ptr, kvrhf) >> \ >> +do { >> \ >> + typeof (ptr) ___p = (ptr); >> \ >> + >> \ >> + if (___p) { >> \ >> + BUILD_BUG_ON(offsetof(typeof(*(ptr)), kvrhf) >= 4096); >> \ >> + kfree_call_rcu_nolock(&((___p)->kvrhf), (void *) (___p)); >> \ >> + } >> \ >> +} while (0) >> + >> /* >> * Place this after a lock-acquisition primitive to guarantee that >> * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies -- Cheers, Harry / Hyeonggon
OpenPGP_signature.asc
Description: OpenPGP digital signature
