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Tue, 22 Sep 2026 05:44:46 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 22 Sep 2026 14:44:44 +0200 To: Ye Liu Cc: Andrew Morton , Uladzislau Rezki , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Ye Liu Subject: Re: [PATCH v2 2/3] mm/vmalloc: fix vmalloc_dump_obj cross-zone VA lookup Message-ID: References: <20260921-vmalloc_dump_obj-v2-0-73fceb3ed1c8@linux.dev> <20260921-vmalloc_dump_obj-v2-2-73fceb3ed1c8@linux.dev> 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: <20260921-vmalloc_dump_obj-v2-2-73fceb3ed1c8@linux.dev> On Mon, Sep 21, 2026 at 09:17:22PM +0800, Ye Liu wrote: > From: Ye Liu > > vmalloc_dump_obj() searches only one vmap node (addr_to_node(addr)), > but a vmalloc allocation may span multiple vmap zones. The VA is > stored in only one node's rb-tree (addr_to_node(va_start)), so an > object pointer in a different zone than va_start maps to a different > node and the search misses. This affects any allocation larger than > vmap_zone_size (64 KiB) on multi-CPU systems. > > Iterate all vmap nodes using for_each_vmap_node, like find_vmap_area() > does, but with spin_trylock instead of spin_lock as this function can > be called from atomic dump contexts (OOM, KASAN, RCU). > > Signed-off-by: Ye Liu > --- > mm/vmalloc.c | 24 ++++++++++++++++++------ > 1 file changed, 18 insertions(+), 6 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index df42d8a6f058..30c610f678dc 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -5278,17 +5278,29 @@ bool vmalloc_dump_obj(void *object) > unsigned long nr_pages; > > addr = PAGE_ALIGN_DOWN((unsigned long) object); > - vn = addr_to_node(addr); > > - if (!spin_trylock(&vn->busy.lock)) > - return false; > + /* > + * A vmalloc allocation may span multiple vmap zones, so the > + * node whose rb-tree holds the VA may differ from the node > + * the address maps to. Search all nodes. Use trylock as > + * this function can be called from atomic dump contexts. > + */ > + va = NULL; > + for_each_vmap_node(vn) { > + if (!spin_trylock(&vn->busy.lock)) > + continue; > + > + va = __find_vmap_area(addr, &vn->busy.root); > + if (va && va->vm) > + break; > > - va = __find_vmap_area(addr, &vn->busy.root); > - if (!va || !va->vm) { > spin_unlock(&vn->busy.lock); > - return false; > + va = NULL; > } > > + if (!va) > + return false; > + > vm = va->vm; > addr = (unsigned long) vm->addr; > caller = vm->caller; > > -- > 2.25.1 > diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 89c327a6ce7d..3719dc02dcaf 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2511,7 +2511,22 @@ static void free_unmap_vmap_area(struct vmap_area *va) free_vmap_area_noflush(va); } -struct vmap_area *find_vmap_area(unsigned long addr) +static inline int next_vmap_node_id(int i) +{ + return (i + nr_vmap_nodes - 1) % nr_vmap_nodes; +} + +enum vmap_lock_mode { + VMAP_LOCK, + VMAP_TRYLOCK, +}; + +/* + * Add a comment here. + */ +static struct vmap_area * +find_vmap_area_lock(unsigned long addr, struct vmap_node **locked_vn, + enum vmap_lock_mode mode) { struct vmap_node *vn; struct vmap_area *va; @@ -2534,16 +2549,40 @@ struct vmap_area *find_vmap_area(unsigned long addr) * addr is within 2 or 0 nodes we should do extra work. */ i = j = addr_to_node_id(addr); + do { vn = &vmap_nodes[i]; - spin_lock(&vn->busy.lock); + if (mode == VMAP_LOCK) { + spin_lock(&vn->busy.lock); + } else { + if (!spin_trylock(&vn->busy.lock)) + continue; + } + va = __find_vmap_area(addr, &vn->busy.root); + if (va) { + *locked_vn = vn; + return va; + } + spin_unlock(&vn->busy.lock); + } while ((i = next_vmap_node_id(i)) != j); - if (va) - return va; - } while ((i = (i + nr_vmap_nodes - 1) % nr_vmap_nodes) != j); + *locked_vn = NULL; + return NULL; +} + +struct vmap_area *find_vmap_area(unsigned long addr) +{ + struct vmap_node *vn; + struct vmap_area *va; + + va = find_vmap_area_lock(addr, &vn, VMAP_LOCK); + if (va) { + spin_unlock(&vn->busy.lock); + return va; + } return NULL; } and we use the helper in the vmalloc_dump_obj()? -- Uladzislau Rezki