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[107.190.31.17]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2d5bb4dfe6dsm30017965ad.18.2026.08.19.10.30.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Aug 2026 10:30:02 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Wed, 19 Aug 2026 13:30:00 -0400 Message-Id: Cc: , "Alexei Starovoitov" , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" , "Martin KaFai Lau" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , "Emil Tsalapatis" , "Ihor Solodrai" , "Yuan Chen" Subject: Re: [PATCH bpf-next v3 3/3] bpf, arena: check range_tree_set return in arena_free_pages and arena_free_worker From: "Emil Tsalapatis" To: , X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260810134800.2875487-1-chenyuan_fl@163.com> <20260810134800.2875487-4-chenyuan_fl@163.com> In-Reply-To: <20260810134800.2875487-4-chenyuan_fl@163.com> On Mon Aug 10, 2026 at 9:48 AM EDT, chenyuan_fl wrote: > From: Yuan Chen > > arena_free_pages() and arena_free_worker() now handle range_tree_set() > errors. arena_free_pages() aborts the free on error, and > arena_free_worker() moves range_tree_set() before PTE clearing so that a > failed tree update leaves the PTEs intact instead of freeing pages that > the arena free tree does not track. > > Also check the range_tree_set() return value in arena_alloc_pages()'s > error path, which restores the unpopulated tail of a partially allocated > range; log a warning instead of silently leaking the virtual range when > the tree update fails. > > Signed-off-by: Yuan Chen Reviewed-by: Emil Tsalapatis The fact we can fail to free a page because of an allocation failure is ...not great. Especially considering the failure is silent (we can't turn this into a warning ofc bc it would be triggerable by user error). Imo this is very close to a silent memory leak, but the only mitigation I can think of is some kind of retry, and going down that route would get really messy really fast. > --- > kernel/bpf/arena.c | 22 ++++++++++++++++++---- > 1 file changed, 18 insertions(+), 4 deletions(-) > > diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c > index 555ee2531ef9..d57a0b617525 100644 > --- a/kernel/bpf/arena.c > +++ b/kernel/bpf/arena.c > @@ -766,7 +766,9 @@ static long arena_alloc_pages(struct bpf_arena *arena= , long uaddr, long page_cnt > bpf_map_memcg_exit(old_memcg, new_memcg); > return clear_lo32(arena->user_vm_start) + uaddr32; > out: > - range_tree_set(&arena->rt, pgoff + mapped, page_cnt - mapped); > + if (range_tree_set(&arena->rt, pgoff + mapped, page_cnt - mapped)) > + pr_warn_ratelimited("bpf_arena: failed to restore free range %ld+%ld a= fter partial alloc\n", > + pgoff + mapped, page_cnt - mapped); > raw_res_spin_unlock_irqrestore(&arena->spinlock, flags); > if (mapped) { > flush_vmap_cache(kern_vm_start + uaddr32, mapped << PAGE_SHIFT); > @@ -881,7 +883,12 @@ static void arena_free_pages(struct bpf_arena *arena= , long uaddr, long page_cnt, > if (ret) > goto defer; > =20 > - range_tree_set(&arena->rt, pgoff, page_cnt); > + ret =3D range_tree_set(&arena->rt, pgoff, page_cnt); > + if (ret) { > + raw_res_spin_unlock_irqrestore(&arena->spinlock, flags); > + bpf_map_memcg_exit(old_memcg, new_memcg); > + return; > + } > =20 > init_llist_head(&free_pages); > cdata.arena =3D arena; > @@ -1004,11 +1011,18 @@ static void arena_free_worker(struct work_struct = *work) > kaddr =3D arena_vm_start + s->uaddr; > pgoff =3D compute_pgoff(arena, s->uaddr); > =20 > + /* > + * Mark the range as free before clearing PTEs so that > + * if the range tree update fails we leave the PTEs > + * intact, avoiding an unrecoverable state where pages > + * are freed but the arena free tree does not track them. > + */ > + if (range_tree_set(&arena->rt, pgoff, page_cnt)) > + continue; > + > /* clear ptes and collect pages in free_pages llist */ > apply_to_existing_page_range(&init_mm, kaddr, page_cnt << PAGE_SHIFT, > apply_range_clear_cb, &cdata); > - > - range_tree_set(&arena->rt, pgoff, page_cnt); > } > raw_res_spin_unlock_irqrestore(&arena->spinlock, flags); > =20