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Sat, 11 Oct 2025 08:45:53 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id QI/kBEEZ6mi3CgAAD6G6ig (envelope-from ); Sat, 11 Oct 2025 08:45:53 +0000 From: Vlastimil Babka Date: Sat, 11 Oct 2025 10:45:41 +0200 Subject: [PATCH] slab: fix barn NULL pointer dereference on memoryless nodes 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="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20251011-null-barn-fix-v1-1-5fe5af5b8fd8@suse.cz> X-B4-Tracking: v=1; b=H4sIADQZ6mgC/6tWKk4tykwtVrJSqFYqSi3LLM7MzwNyDHUUlJIzE vPSU3UzU4B8JSMDI1NDA0ND3bzSnBzdpMSiPN20zArdRGNzM1MLM6MUgzQTJaCegqJUoDDYvOj Y2loArihwS18AAAA= X-Change-ID: 20251011-null-barn-fix-a3765862d0f4 To: Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Suren Baghdasaryan Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Linus Torvalds , Phil Auld , Vlastimil Babka X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; 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MIME_TRACE(0.00)[0:+]; RCPT_COUNT_SEVEN(0.00)[11]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; URIBL_BLOCKED(0.00)[imap1.dmz-prg2.suse.org:helo]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Flag: NO X-Spam-Score: -4.30 X-Spam-Level: Phil reported a boot failure once sheaves become used in commits 59faa4da7cd4 ("maple_tree: use percpu sheaves for maple_node_cache") and 3accabda4da1 ("mm, vma: use percpu sheaves for vm_area_struct cache"): BUG: kernel NULL pointer dereference, address: 0000000000000040 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: Oops: 0000 [#1] SMP NOPTI CPU: 21 UID: 0 PID: 818 Comm: kworker/u398:0 Not tainted 6.17.0-rc3.slab+ = #5 PREEMPT(voluntary) Hardware name: Dell Inc. PowerEdge R7425/02MJ3T, BIOS 1.26.0 07/30/2025 RIP: 0010:__pcs_replace_empty_main+0x44/0x1d0 Code: ec 08 48 8b 46 10 48 8b 76 08 48 85 c0 74 0b 8b 48 18 85 c9 0f 85 e5= 00 00 00 65 48 63 05 e4 ee 50 02 49 8b 84 c6 e0 00 00 00 <4c> 8b 68 40 4c = 89 ef e8 b0 81 ff ff 48 89 c5 48 85 c0 74 1d 48 89 RSP: 0018:ffffd2d10950bdb0 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff8a775dab74b0 RCX: 00000000ffffffff RDX: 0000000000000cc0 RSI: ffff8a6800804000 RDI: ffff8a680004e300 RBP: ffffd2d10950be40 R08: 0000000000000060 R09: ffffffffb9367388 R10: 00000000000149e8 R11: ffff8a6f87a38000 R12: 0000000000000cc0 R13: 0000000000000cc0 R14: ffff8a680004e300 R15: 00000000000000c0 FS: 0000000000000000(0000) GS:ffff8a77a3541000(0000) knlGS:00000000000000= 00 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000040 CR3: 0000000e1aa24000 CR4: 00000000003506f0 Call Trace: ? srso_return_thunk+0x5/0x5f ? vm_area_alloc+0x1e/0x60 kmem_cache_alloc_noprof+0x4ec/0x5b0 vm_area_alloc+0x1e/0x60 create_init_stack_vma+0x26/0x210 alloc_bprm+0x139/0x200 kernel_execve+0x4a/0x140 call_usermodehelper_exec_async+0xd0/0x190 ? __pfx_call_usermodehelper_exec_async+0x10/0x10 ret_from_fork+0xf0/0x110 ? __pfx_call_usermodehelper_exec_async+0x10/0x10 ret_from_fork_asm+0x1a/0x30 Modules linked in: CR2: 0000000000000040 ---[ end trace 0000000000000000 ]--- RIP: 0010:__pcs_replace_empty_main+0x44/0x1d0 Code: ec 08 48 8b 46 10 48 8b 76 08 48 85 c0 74 0b 8b 48 18 85 c9 0f 85 e5= 00 00 00 65 48 63 05 e4 ee 50 02 49 8b 84 c6 e0 00 00 00 <4c> 8b 68 40 4c = 89 ef e8 b0 81 ff ff 48 89 c5 48 85 c0 74 1d 48 89 RSP: 0018:ffffd2d10950bdb0 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff8a775dab74b0 RCX: 00000000ffffffff RDX: 0000000000000cc0 RSI: ffff8a6800804000 RDI: ffff8a680004e300 RBP: ffffd2d10950be40 R08: 0000000000000060 R09: ffffffffb9367388 R10: 00000000000149e8 R11: ffff8a6f87a38000 R12: 0000000000000cc0 R13: 0000000000000cc0 R14: ffff8a680004e300 R15: 00000000000000c0 FS: 0000000000000000(0000) GS:ffff8a77a3541000(0000) knlGS:00000000000000= 00 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000040 CR3: 0000000e1aa24000 CR4: 00000000003506f0 Kernel panic - not syncing: Fatal exception Kernel Offset: 0x36a00000 from 0xffffffff81000000 (relocation range: 0xfff= fffff80000000-0xffffffffbfffffff) ---[ end Kernel panic - not syncing: Fatal exception ]--- And noted "this is an AMD EPYC 7401 with 8 NUMA nodes configured such that memory is only on 2 of them." # numactl --hardware available: 8 nodes (0-7) node 0 cpus: 0 8 16 24 32 40 48 56 64 72 80 88 node 0 size: 0 MB node 0 free: 0 MB node 1 cpus: 2 10 18 26 34 42 50 58 66 74 82 90 node 1 size: 31584 MB node 1 free: 30397 MB node 2 cpus: 4 12 20 28 36 44 52 60 68 76 84 92 node 2 size: 0 MB node 2 free: 0 MB node 3 cpus: 6 14 22 30 38 46 54 62 70 78 86 94 node 3 size: 0 MB node 3 free: 0 MB node 4 cpus: 1 9 17 25 33 41 49 57 65 73 81 89 node 4 size: 0 MB node 4 free: 0 MB node 5 cpus: 3 11 19 27 35 43 51 59 67 75 83 91 node 5 size: 32214 MB node 5 free: 31625 MB node 6 cpus: 5 13 21 29 37 45 53 61 69 77 85 93 node 6 size: 0 MB node 6 free: 0 MB node 7 cpus: 7 15 23 31 39 47 55 63 71 79 87 95 node 7 size: 0 MB node 7 free: 0 MB Linus decoded the stacktrace to get_barn() and get_node() and determined that kmem_cache->node[numa_mem_id()] is NULL. The problem is due to a wrong assumption that memoryless nodes only exist on systems with CONFIG_HAVE_MEMORYLESS_NODES, where numa_mem_id() points to the nearest node that has memory. SLUB has been allocating its kmem_cache_node structures only on nodes with memory and so it does with struct node_barn. For kmem_cache_node, get_partial_node() checks if get_node() result is not NULL, which I assumed was for protection from a bogus node id passed to kmalloc_node() but apparently it's also for systems where numa_mem_id() (used when no specific node is given) might return a memoryless node. Fix the sheaves code the same way by checking the result of get_node() and bailing out if it's NULL. Note that cpus on such memoryless nodes will have degraded sheaves performance, which can be improved later, preferably by making numa_mem_id() work properly on such systems. Fixes: 2d517aa09bbc ("slab: add opt-in caching layer of percpu sheaves") Reported-and-tested-by: Phil Auld Closes: https://lore.kernel.org/all/20251010151116.GA436967@pauld.westford.= csb/ Analyzed-by: Linus Torvalds Link: https://lore.kernel.org/all/CAHk-%3Dwg1xK%2BBr%3DFJ5QipVhzCvq7uQVPt5P= rze6HDhQQ%3DQD_BcQ@mail.gmail.com/ Signed-off-by: Vlastimil Babka Reviewed-by: Harry Yoo --- mm/slub.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++----------= ---- 1 file changed, 51 insertions(+), 14 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 135c408e0515..b1f15598fbfd 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -504,10 +504,18 @@ static inline struct kmem_cache_node *get_node(struct= kmem_cache *s, int node) return s->node[node]; } =20 -/* Get the barn of the current cpu's memory node */ +/* + * Get the barn of the current cpu's closest memory node. It may not exist= on + * systems with memoryless nodes but without CONFIG_HAVE_MEMORYLESS_NODES + */ static inline struct node_barn *get_barn(struct kmem_cache *s) { - return get_node(s, numa_mem_id())->barn; + struct kmem_cache_node *n =3D get_node(s, numa_mem_id()); + + if (!n) + return NULL; + + return n->barn; } =20 /* @@ -4982,6 +4990,10 @@ __pcs_replace_empty_main(struct kmem_cache *s, struc= t slub_percpu_sheaves *pcs, } =20 barn =3D get_barn(s); + if (!barn) { + local_unlock(&s->cpu_sheaves->lock); + return NULL; + } =20 full =3D barn_replace_empty_sheaf(barn, pcs->main); =20 @@ -5153,13 +5165,20 @@ unsigned int alloc_from_pcs_bulk(struct kmem_cache = *s, size_t size, void **p) if (unlikely(pcs->main->size =3D=3D 0)) { =20 struct slab_sheaf *full; + struct node_barn *barn; =20 if (pcs->spare && pcs->spare->size > 0) { swap(pcs->main, pcs->spare); goto do_alloc; } =20 - full =3D barn_replace_empty_sheaf(get_barn(s), pcs->main); + barn =3D get_barn(s); + if (!barn) { + local_unlock(&s->cpu_sheaves->lock); + return allocated; + } + + full =3D barn_replace_empty_sheaf(barn, pcs->main); =20 if (full) { stat(s, BARN_GET); @@ -5314,6 +5333,7 @@ kmem_cache_prefill_sheaf(struct kmem_cache *s, gfp_t = gfp, unsigned int size) { struct slub_percpu_sheaves *pcs; struct slab_sheaf *sheaf =3D NULL; + struct node_barn *barn; =20 if (unlikely(size > s->sheaf_capacity)) { =20 @@ -5355,8 +5375,11 @@ kmem_cache_prefill_sheaf(struct kmem_cache *s, gfp_t= gfp, unsigned int size) pcs->spare =3D NULL; stat(s, SHEAF_PREFILL_FAST); } else { + barn =3D get_barn(s); + stat(s, SHEAF_PREFILL_SLOW); - sheaf =3D barn_get_full_or_empty_sheaf(get_barn(s)); + if (barn) + sheaf =3D barn_get_full_or_empty_sheaf(barn); if (sheaf && sheaf->size) stat(s, BARN_GET); else @@ -5426,7 +5449,7 @@ void kmem_cache_return_sheaf(struct kmem_cache *s, gf= p_t gfp, * If the barn has too many full sheaves or we fail to refill the sheaf, * simply flush and free it. */ - if (data_race(barn->nr_full) >=3D MAX_FULL_SHEAVES || + if (!barn || data_race(barn->nr_full) >=3D MAX_FULL_SHEAVES || refill_sheaf(s, sheaf, gfp)) { sheaf_flush_unused(s, sheaf); free_empty_sheaf(s, sheaf); @@ -5943,10 +5966,9 @@ static void __slab_free(struct kmem_cache *s, struct= slab *slab, * put the full sheaf there. */ static void __pcs_install_empty_sheaf(struct kmem_cache *s, - struct slub_percpu_sheaves *pcs, struct slab_sheaf *empty) + struct slub_percpu_sheaves *pcs, struct slab_sheaf *empty, + struct node_barn *barn) { - struct node_barn *barn; - lockdep_assert_held(this_cpu_ptr(&s->cpu_sheaves->lock)); =20 /* This is what we expect to find if nobody interrupted us. */ @@ -5956,8 +5978,6 @@ static void __pcs_install_empty_sheaf(struct kmem_cac= he *s, return; } =20 - barn =3D get_barn(s); - /* * Unlikely because if the main sheaf had space, we would have just * freed to it. Get rid of our empty sheaf. @@ -6002,6 +6022,11 @@ __pcs_replace_full_main(struct kmem_cache *s, struct= slub_percpu_sheaves *pcs) lockdep_assert_held(this_cpu_ptr(&s->cpu_sheaves->lock)); =20 barn =3D get_barn(s); + if (!barn) { + local_unlock(&s->cpu_sheaves->lock); + return NULL; + } + put_fail =3D false; =20 if (!pcs->spare) { @@ -6084,7 +6109,7 @@ __pcs_replace_full_main(struct kmem_cache *s, struct = slub_percpu_sheaves *pcs) } =20 pcs =3D this_cpu_ptr(s->cpu_sheaves); - __pcs_install_empty_sheaf(s, pcs, empty); + __pcs_install_empty_sheaf(s, pcs, empty, barn); =20 return pcs; } @@ -6121,8 +6146,9 @@ bool free_to_pcs(struct kmem_cache *s, void *object) =20 static void rcu_free_sheaf(struct rcu_head *head) { + struct kmem_cache_node *n; struct slab_sheaf *sheaf; - struct node_barn *barn; + struct node_barn *barn =3D NULL; struct kmem_cache *s; =20 sheaf =3D container_of(head, struct slab_sheaf, rcu_head); @@ -6139,7 +6165,11 @@ static void rcu_free_sheaf(struct rcu_head *head) */ __rcu_free_sheaf_prepare(s, sheaf); =20 - barn =3D get_node(s, sheaf->node)->barn; + n =3D get_node(s, sheaf->node); + if (!n) + goto flush; + + barn =3D n->barn; =20 /* due to slab_free_hook() */ if (unlikely(sheaf->size =3D=3D 0)) @@ -6157,11 +6187,12 @@ static void rcu_free_sheaf(struct rcu_head *head) return; } =20 +flush: stat(s, BARN_PUT_FAIL); sheaf_flush_unused(s, sheaf); =20 empty: - if (data_race(barn->nr_empty) < MAX_EMPTY_SHEAVES) { + if (barn && data_race(barn->nr_empty) < MAX_EMPTY_SHEAVES) { barn_put_empty_sheaf(barn, sheaf); return; } @@ -6191,6 +6222,10 @@ bool __kfree_rcu_sheaf(struct kmem_cache *s, void *o= bj) } =20 barn =3D get_barn(s); + if (!barn) { + local_unlock(&s->cpu_sheaves->lock); + goto fail; + } =20 empty =3D barn_get_empty_sheaf(barn); =20 @@ -6304,6 +6339,8 @@ static void free_to_pcs_bulk(struct kmem_cache *s, si= ze_t size, void **p) goto do_free; =20 barn =3D get_barn(s); + if (!barn) + goto no_empty; =20 if (!pcs->spare) { empty =3D barn_get_empty_sheaf(barn); --- base-commit: f76b1683d16dcd5299a9b67d8ef45fe8d29cb2e6 change-id: 20251011-null-barn-fix-a3765862d0f4 Best regards, --=20 Vlastimil Babka