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Mon, 27 Apr 2026 09:19:02 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Mon, 27 Apr 2026 18:19:00 +0200 To: Vlastimil Babka Cc: Uladzislau Rezki , Herbert Xu , Harry Yoo , Hao Li , Thomas Graf , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Andrew Morton , Michal Hocko , Baoquan He , Alexander Potapenko , Andrey Ryabinin , Marco Elver , Michal Hocko , linux-mm@kvack.org Subject: Re: [linus:master] [mm] c6307674ed: BUG:sleeping_function_called_from_invalid_context_at_mm/vmalloc.c Message-ID: References: <202604211323.fac1b29e-lkp@intel.com> <4e269fb1-cd6c-46ca-ac2a-168ce9fd06fe@suse.com> <6cae0418-eabe-4864-b87f-b1f953de06b0@suse.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6cae0418-eabe-4864-b87f-b1f953de06b0@suse.com> On Mon, Apr 27, 2026 at 04:37:11PM +0200, Vlastimil Babka wrote: > On 4/27/26 16:17, Uladzislau Rezki wrote: > > On Mon, Apr 27, 2026 at 10:53:52AM +0200, Vlastimil Babka wrote: > >> On 4/23/26 05:34, Herbert Xu wrote: > >> > On Wed, Apr 22, 2026 at 10:32:16AM +0200, Uladzislau Rezki wrote: > >> >> > >> >> We have added non-sleeping flags for vmalloc() to extend kvmalloc() > >> >> functionality as folk need those. > >> >> > >> >> Another option, would be: always use vfree_atomic() from the kvfree() > >> >> path. > >> >> > >> >> Any thoughts? > >> > > >> > Perhaps add a kvfree_atomic that just calls vfree_atomic? > >> > >> kvfree()'s comment says > >> > >> " * Context: Either preemptible task context or not-NMI interrupt." > >> > > I am not sure the description clearly reflects the intended usage. > > To me it sounds like all contexts but excluding NMI. > > Agree it's not clear, my immediate reaction was the same and took me a bit > to understand. > > > For example, calling this under spin_lock() will be invalid, as > > the vfree() path may invoke cond_resched(). > > Yeah, it's covered by the "preemptible" word, but not super clear. > IIUC it all boils down to this in vfree(): > > > if (unlikely(in_interrupt())) { > vfree_atomic(addr); > return; > } > > Which can do the right thing in an interrupt, but obviously cannot > automatically recognize the "under spin_lock()" situation. > > So I don't think we can change it now with all the existing callers, but if > a better wording exists, we could make the comment more clear. > > >> so this is neither. It might be ok then to create kvfree_atomic(). Always > >> using vfree_atomic() from kvfree() might be wasteful. > >> > >> > For rhashtable it really makes no difference either way. But it > >> > would eliminate the unsightly call to is_vmalloc_addr in rhashtable. > >> > > > Seems atomic version makes sense here: > > > > > > diff --git a/include/linux/slab.h b/include/linux/slab.h > > index 15a60b501b95..2b5ab488e96b 100644 > > --- a/include/linux/slab.h > > +++ b/include/linux/slab.h > > @@ -1234,6 +1234,9 @@ void *kvrealloc_node_align_noprof(const void *p, size_t size, unsigned long alig > > extern void kvfree(const void *addr); > > DEFINE_FREE(kvfree, void *, if (!IS_ERR_OR_NULL(_T)) kvfree(_T)) > > > > +extern void kvfree_atomic(const void *addr); > > +DEFINE_FREE(kvfree_atomic, void *, if (!IS_ERR_OR_NULL(_T)) kvfree_atomic(_T)) > > + > > extern void kvfree_sensitive(const void *addr, size_t len); > > > > unsigned int kmem_cache_size(struct kmem_cache *s); > > diff --git a/mm/slub.c b/mm/slub.c > > index 2b2d33cc735c..e25a0eab6ff7 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -6802,6 +6802,22 @@ void kvfree(const void *addr) > > } > > EXPORT_SYMBOL(kvfree); > > > > +/** > > + * kvfree_atomic() - Free memory. > > + * @addr: Pointer to allocated memory. > > + * > > + * Same as kvfree(), but safe to use in atomic contexts. > > + * Must not be called from NMI context. > > + */ > > +void kvfree_atomic(const void *addr) > > +{ > > + if (is_vmalloc_addr(addr)) > > + vfree_atomic(addr); > > + else > > + kfree(addr); > > +} > > +EXPORT_SYMBOL(kvfree_atomic); > > + > > /** > > * kvfree_sensitive - Free a data object containing sensitive information. > > * @addr: address of the data object to be freed. > > > > > > I can post it if no objections. > > LGTM but also should be now used in rhashtable_try_insert() I think? > Like below: rhashtable_try_insert() rhashtable_insert_rehash() bucket_table_free_atomic(new_tbl); the patch for rhashtable.c can look like: diff --git a/lib/rhashtable.c b/lib/rhashtable.c index 6074ed5f66f3..4111aab8cee4 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -114,6 +114,14 @@ static void bucket_table_free(const struct bucket_table *tbl) kvfree(tbl); } +static void bucket_table_free_atomic(const struct bucket_table *tbl) +{ + if (tbl->nest) + nested_bucket_table_free(tbl); + + kvfree_atomic(tbl); +} + static void bucket_table_free_rcu(struct rcu_head *head) { bucket_table_free(container_of(head, struct bucket_table, rcu)); @@ -473,7 +481,7 @@ static int rhashtable_insert_rehash(struct rhashtable *ht, err = rhashtable_rehash_attach(ht, tbl, new_tbl); if (err) { - bucket_table_free(new_tbl); + bucket_table_free_atomic(new_tbl); if (err == -EEXIST) err = 0; } else -- Uladzislau Rezki