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([2001:1a48:8:903:1ed6:4f73:ce38:f9d4]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43fe4cb135asm86796551f8f.6.2026.04.27.07.37.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Apr 2026 07:37:12 -0700 (PDT) Message-ID: <6cae0418-eabe-4864-b87f-b1f953de06b0@suse.com> Date: Mon, 27 Apr 2026 16:37:11 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [linus:master] [mm] c6307674ed: BUG:sleeping_function_called_from_invalid_context_at_mm/vmalloc.c Content-Language: en-US To: Uladzislau Rezki Cc: 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 References: <202604211323.fac1b29e-lkp@intel.com> <4e269fb1-cd6c-46ca-ac2a-168ce9fd06fe@suse.com> From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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? > > -- > Uladzislau Rezki