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Thu, 16 Mar 2023 05:12:27 -0700 (PDT) Date: Thu, 16 Mar 2023 12:12:22 +0000 From: Mark Rutland To: Pavel Begunkov , Jens Axboe Cc: io-uring@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH for-next 4/4] io_uring/rsrc: optimise registered huge pages Message-ID: References: <757a0c399774f23df5dbfe2e0cc79f7ea432b04c.1677041932.git.asml.silence@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <757a0c399774f23df5dbfe2e0cc79f7ea432b04c.1677041932.git.asml.silence@gmail.com> Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org Hi, Since v6.3-rc1, when fuzzing arm64 with Syzkaller, I see a bunch of bad page state splats with either "nonzero pincount" or "nonzero compound_pincount", and bisecting led me to this patch / commit: 57bebf807e2abcf8 ("io_uring/rsrc: optimise registered huge pages") The splats look like: | BUG: Bad page state in process kworker/u8:0 pfn:5c001 | page:00000000bfda61c8 refcount:0 mapcount:0 mapping:0000000000000000 index:0x20001 pfn:0x5c001 | head:0000000011409842 order:9 entire_mapcount:0 nr_pages_mapped:0 pincount:1 | anon flags: 0x3fffc00000b0004(uptodate|head|mappedtodisk|swapbacked|node=0|zone=0|lastcpupid=0xffff) | raw: 03fffc0000000000 fffffc0000700001 ffffffff00700903 0000000100000000 | raw: 0000000000000200 0000000000000000 00000000ffffffff 0000000000000000 | head: 03fffc00000b0004 dead000000000100 dead000000000122 ffff00000a809dc1 | head: 0000000000020000 0000000000000000 00000000ffffffff 0000000000000000 | page dumped because: nonzero pincount | CPU: 3 PID: 9 Comm: kworker/u8:0 Not tainted 6.3.0-rc2-00001-gc6811bf0cd87 #1 | Hardware name: linux,dummy-virt (DT) | Workqueue: events_unbound io_ring_exit_work | Call trace: | dump_backtrace+0x13c/0x208 | show_stack+0x34/0x58 | dump_stack_lvl+0x150/0x1a8 | dump_stack+0x20/0x30 | bad_page+0xec/0x238 | free_tail_pages_check+0x280/0x350 | free_pcp_prepare+0x60c/0x830 | free_unref_page+0x50/0x498 | free_compound_page+0xcc/0x100 | free_transhuge_page+0x1f0/0x2b8 | destroy_large_folio+0x80/0xc8 | __folio_put+0xc4/0xf8 | gup_put_folio+0xd0/0x250 | unpin_user_page+0xcc/0x128 | io_buffer_unmap+0xec/0x2c0 | __io_sqe_buffers_unregister+0xa4/0x1e0 | io_ring_exit_work+0x68c/0x1188 | process_one_work+0x91c/0x1a58 | worker_thread+0x48c/0xe30 | kthread+0x278/0x2f0 | ret_from_fork+0x10/0x20 Syzkaller gave me a reliable C reproducer, which I used to bisect (note: DEBUG_VM needs to be selected): | // autogenerated by syzkaller (https://github.com/google/syzkaller) | | #define _GNU_SOURCE | | #include | #include | #include | #include | #include | #include | #include | #include | #include | | #ifndef __NR_io_uring_register | #define __NR_io_uring_register 427 | #endif | #ifndef __NR_io_uring_setup | #define __NR_io_uring_setup 425 | #endif | #ifndef __NR_mmap | #define __NR_mmap 222 | #endif | | #define SIZEOF_IO_URING_SQE 64 | #define SIZEOF_IO_URING_CQE 16 | #define SQ_HEAD_OFFSET 0 | #define SQ_TAIL_OFFSET 64 | #define SQ_RING_MASK_OFFSET 256 | #define SQ_RING_ENTRIES_OFFSET 264 | #define SQ_FLAGS_OFFSET 276 | #define SQ_DROPPED_OFFSET 272 | #define CQ_HEAD_OFFSET 128 | #define CQ_TAIL_OFFSET 192 | #define CQ_RING_MASK_OFFSET 260 | #define CQ_RING_ENTRIES_OFFSET 268 | #define CQ_RING_OVERFLOW_OFFSET 284 | #define CQ_FLAGS_OFFSET 280 | #define CQ_CQES_OFFSET 320 | | struct io_sqring_offsets { | uint32_t head; | uint32_t tail; | uint32_t ring_mask; | uint32_t ring_entries; | uint32_t flags; | uint32_t dropped; | uint32_t array; | uint32_t resv1; | uint64_t resv2; | }; | | struct io_cqring_offsets { | uint32_t head; | uint32_t tail; | uint32_t ring_mask; | uint32_t ring_entries; | uint32_t overflow; | uint32_t cqes; | uint64_t resv[2]; | }; | | struct io_uring_params { | uint32_t sq_entries; | uint32_t cq_entries; | uint32_t flags; | uint32_t sq_thread_cpu; | uint32_t sq_thread_idle; | uint32_t features; | uint32_t resv[4]; | struct io_sqring_offsets sq_off; | struct io_cqring_offsets cq_off; | }; | | #define IORING_OFF_SQ_RING 0 | #define IORING_OFF_SQES 0x10000000ULL | | static long syz_io_uring_setup(volatile long a0, volatile long a1, volatile long a2, volatile long a3, volatile long a4, volatile long a5) | { | uint32_t entries = (uint32_t)a0; | struct io_uring_params* setup_params = (struct io_uring_params*)a1; | void* vma1 = (void*)a2; | void* vma2 = (void*)a3; | void** ring_ptr_out = (void**)a4; | void** sqes_ptr_out = (void**)a5; | uint32_t fd_io_uring = syscall(__NR_io_uring_setup, entries, setup_params); | uint32_t sq_ring_sz = setup_params->sq_off.array + setup_params->sq_entries * sizeof(uint32_t); | uint32_t cq_ring_sz = setup_params->cq_off.cqes + setup_params->cq_entries * SIZEOF_IO_URING_CQE; | uint32_t ring_sz = sq_ring_sz > cq_ring_sz ? sq_ring_sz : cq_ring_sz; | *ring_ptr_out = mmap(vma1, ring_sz, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_POPULATE | MAP_FIXED, fd_io_uring, IORING_OFF_SQ_RING); | uint32_t sqes_sz = setup_params->sq_entries * SIZEOF_IO_URING_SQE; | *sqes_ptr_out = mmap(vma2, sqes_sz, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_POPULATE | MAP_FIXED, fd_io_uring, IORING_OFF_SQES); | return fd_io_uring; | } | | uint64_t r[1] = {0xffffffffffffffff}; | | int main(void) | { | syscall(__NR_mmap, 0x1ffff000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul); | syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 0ul); | syscall(__NR_mmap, 0x21000000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul); | intptr_t res = 0; | *(uint32_t*)0x20000684 = 0; | *(uint32_t*)0x20000688 = 0; | *(uint32_t*)0x2000068c = 0; | *(uint32_t*)0x20000690 = 0; | *(uint32_t*)0x20000698 = -1; | memset((void*)0x2000069c, 0, 12); | res = -1; | res = syz_io_uring_setup(0x2fd6, 0x20000680, 0x20ffd000, 0x20ffc000, 0x20000700, 0x20000740); | if (res != -1) | r[0] = res; | *(uint64_t*)0x20002840 = 0; | *(uint64_t*)0x20002848 = 0; | *(uint64_t*)0x20002850 = 0x20000840; | *(uint64_t*)0x20002858 = 0x1000; | syscall(__NR_io_uring_register, r[0], 0ul, 0x20002840ul, 2ul); | return 0; | } Thanks, Mark. On Wed, Feb 22, 2023 at 02:36:51PM +0000, Pavel Begunkov wrote: > When registering huge pages, internally io_uring will split them into > many PAGE_SIZE bvec entries. That's bad for performance as drivers need > to eventually dma-map the data and will do it individually for each bvec > entry. Coalesce huge pages into one large bvec. > > Signed-off-by: Pavel Begunkov > --- > io_uring/rsrc.c | 38 ++++++++++++++++++++++++++++++++------ > 1 file changed, 32 insertions(+), 6 deletions(-) > > diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c > index ebbd2cea7582..aab1bc6883e9 100644 > --- a/io_uring/rsrc.c > +++ b/io_uring/rsrc.c > @@ -1210,6 +1210,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov, > unsigned long off; > size_t size; > int ret, nr_pages, i; > + struct folio *folio; > > *pimu = ctx->dummy_ubuf; > if (!iov->iov_base) > @@ -1224,6 +1225,21 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov, > goto done; > } > > + /* If it's a huge page, try to coalesce them into a single bvec entry */ > + if (nr_pages > 1) { > + folio = page_folio(pages[0]); > + for (i = 1; i < nr_pages; i++) { > + if (page_folio(pages[i]) != folio) { > + folio = NULL; > + break; > + } > + } > + if (folio) { > + folio_put_refs(folio, nr_pages - 1); > + nr_pages = 1; > + } > + } > + > imu = kvmalloc(struct_size(imu, bvec, nr_pages), GFP_KERNEL); > if (!imu) > goto done; > @@ -1236,6 +1252,17 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov, > > off = (unsigned long) iov->iov_base & ~PAGE_MASK; > size = iov->iov_len; > + /* store original address for later verification */ > + imu->ubuf = (unsigned long) iov->iov_base; > + imu->ubuf_end = imu->ubuf + iov->iov_len; > + imu->nr_bvecs = nr_pages; > + *pimu = imu; > + ret = 0; > + > + if (folio) { > + bvec_set_page(&imu->bvec[0], pages[0], size, off); > + goto done; > + } > for (i = 0; i < nr_pages; i++) { > size_t vec_len; > > @@ -1244,12 +1271,6 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov, > off = 0; > size -= vec_len; > } > - /* store original address for later verification */ > - imu->ubuf = (unsigned long) iov->iov_base; > - imu->ubuf_end = imu->ubuf + iov->iov_len; > - imu->nr_bvecs = nr_pages; > - *pimu = imu; > - ret = 0; > done: > if (ret) > kvfree(imu); > @@ -1364,6 +1385,11 @@ int io_import_fixed(int ddir, struct iov_iter *iter, > const struct bio_vec *bvec = imu->bvec; > > if (offset <= bvec->bv_len) { > + /* > + * Note, huge pages buffers consists of one large > + * bvec entry and should always go this way. The other > + * branch doesn't expect non PAGE_SIZE'd chunks. > + */ > iter->bvec = bvec; > iter->nr_segs = bvec->bv_len; > iter->count -= offset; > -- > 2.39.1 > >