On Tue, Mar 19, 2024 at 10:33 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > On Tue, Mar 19, 2024 at 10:15:43AM +1300, Barry Song wrote: > > On Tue, Mar 19, 2024 at 10:10 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > > > > > On Mon, Mar 18, 2024 at 01:17:19PM -0700, Yosry Ahmed wrote: > > > > On Mon, Mar 18, 2024 at 11:00 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote: > > > > > > > > > > On Mon, Mar 18, 2024 at 9:58 AM syzbot > > > > > <syzbot+adbc983a1588b7805de3@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > Hello, > > > > > > > > > > > > syzbot found the following issue on: > > > > > > > > > > > > HEAD commit: e5eb28f6d1af Merge tag 'mm-nonmm-stable-2024-03-14-09-36' .. > > > > > > git tree: upstream > > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=13043abe180000 > > > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=19bb57c23dffc38e > > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=adbc983a1588b7805de3 > > > > > > compiler: arm-linux-gnueabi-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > > > > > > userspace arch: arm > > > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1706d231180000 > > > > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13ba7959180000 > > > > > > > > > > > > Downloadable assets: > > > > > > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/8ead8862021c/non_bootable_disk-e5eb28f6.raw.xz > > > > > > vmlinux: https://storage.googleapis.com/syzbot-assets/0a7371c63ff2/vmlinux-e5eb28f6.xz > > > > > > kernel image: https://storage.googleapis.com/syzbot-assets/7539441b4add/zImage-e5eb28f6.xz > > > > > > > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > > > > Reported-by: syzbot+adbc983a1588b7805de3@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > > > > > > > ------------[ cut here ]------------ > > > > > > kernel BUG at include/linux/scatterlist.h:187! > > > > > > > > > > Looks like the provided buffer is invalid: > > > > > > > > > > #ifdef CONFIG_DEBUG_SG > > > > > BUG_ON(!virt_addr_valid(buf)); > > > > > #endif > > > > > > > > > > which is "src" from: > > > > > > > > > > sg_init_one(&input, src, entry->length); > > > > > > > > > > Looking at the surrounding code and recent history, there's this > > > > > commit that stands out: > > > > > > > > > > mm/zswap: remove the memcpy if acomp is not sleepable > > > > > (sha: 270700dd06ca41a4779c19eb46608f076bb7d40e) > > > > > > > > > > which has the effect of, IIUC, using the zpool mapped memory directly > > > > > as src, instead of acomp_ctx->buffer (which was previously the case, > > > > > as zsmalloc was not sleepable). > > > > > > > > > > This might not necessarily be a bug with that commit itself, but might > > > > > have revealed another bug elsewhere. > > > > > > > > > > Anyway, cc-ing the author, Barry Song, to fact check me :) Will take a > > > > > closer look later. > > > > > > > > I am not a highmem expert, but the reproducer has CONFIG_HIGHMEM=y, > > > > and it seems like zs_map_object() may return a highmem address if the > > > > compressed object is entirely in a single page to avoid copying to a > > > > buffer: > > > > > > > > if (off + class->size <= PAGE_SIZE) { > > > > /* this object is contained entirely within a page */ > > > > area->vm_addr = kmap_atomic(page); > > > > ret = area->vm_addr + off; > > > > goto out; > > > > } > > > > > > > > The virt_addr_valid() check seems to indicate that we expect a direct > > > > map address in sg_init_one(), right? > > > > > > If the page is highmem, kmap_atomic() establishes a temporary mapping > > > to it in the direct map, such that we have a legit kernel pointer to > > > the memory. Otherwise the memcpy() in zswap also wouldn't work... Am I > > > missing something? > > > > Right, we built a map but it is not a linear mapping. so we can't use > > virt_to_page > > on this kind of non-linear mapping. > > kmap_to_page can handle both linear and non-linear, but Ira's commit > > added a WARN_ON_ONCE in it for non-linear mapping case. > > Ah, I misread what virt_addr_valid() does. It actually excludes > kmap. Which, yes, makes sense, if the next line does virt_to_page()... > > Sorry about the noise. no worries. I just wonder why Ira's commit ef6e06b2ef870 has added a WARN_ON_ONCE in kmap_to_page() given we still have many users :-) drivers/fpga/fpga-mgr.c: pages[index] = kmap_to_page((void *)p); drivers/spi/spi.c: vm_page = kmap_to_page(buf); drivers/vfio/pci/pds/lm.c: pages[i] = kmap_to_page((void *)p); fs/erofs/data.c: .page = kmap_to_page(ptr), fs/smb/server/transport_rdma.c: page = kmap_to_page(buf); net/9p/trans_virtio.c: (*pages)[index] = kmap_to_page(p);
