From 0da478369b6eb19dca4b6810f15f36a6ac0fe615 Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Tue, 6 Oct 2020 14:53:06 -0400 Subject: [PATCH] UPSTREAM: virtiofs: calculate number of scatter-gather elements accurately virtiofs currently maps various buffers in scatter gather list and it looks at number of pages (ap->pages) and assumes that same number of pages will be used both for input and output (sg_count_fuse_req()), and calculates total number of scatterlist elements accordingly. But looks like this assumption is not valid in all the cases. For example, Cai Qian reported that trinity, triggers warning with virtiofs sometimes. A closer look revealed that if one calls ioctl(fd, 0x5a004000, buf), it will trigger following warning. WARN_ON(out_sgs + in_sgs != total_sgs) In this case, total_sgs = 8, out_sgs=4, in_sgs=3. Number of pages is 2 (ap->pages), but out_sgs are using both the pages but in_sgs are using only one page. In this case, fuse_do_ioctl() sets different size values for input and output. args->in_args[args->in_numargs - 1].size == 6656 args->out_args[args->out_numargs - 1].size == 4096 So current method of calculating how many scatter-gather list elements will be used is not accurate. Make calculations more precise by parsing size and ap->descs. Reported-by: Qian Cai Change-Id: I1ccdbce4b946a016a4a8faea234de0cb470825ac Signed-off-by: Vivek Goyal Link: https://lore.kernel.org/linux-fsdevel/5ea77e9f6cb8c2db43b09fbd4158ab2d8c066a0a.camel@redhat.com/ Reviewed-by: Stefan Hajnoczi Signed-off-by: Miklos Szeredi --- fs/fuse/virtio_fs.c | 32 +++++++++++++++++++++++++++----- 1 file changed, 27 insertions(+), 5 deletions(-) diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c index 071917737a2d..ed576fdc6da0 100644 --- a/fs/fuse/virtio_fs.c +++ b/fs/fuse/virtio_fs.c @@ -1033,18 +1033,37 @@ __releases(fiq->lock) spin_unlock(&fiq->lock); } +/* Count number of scatter-gather elements required */ +static unsigned int sg_count_fuse_pages(struct fuse_page_desc *page_descs, + unsigned int num_pages, + unsigned int total_len) +{ + unsigned int i; + unsigned int this_len; + + for (i = 0; i < num_pages && total_len; i++) { + this_len = min(page_descs[i].length, total_len); + total_len -= this_len; + } + + return i; +} + /* Return the number of scatter-gather list elements required */ static unsigned int sg_count_fuse_req(struct fuse_req *req) { struct fuse_args *args = req->args; struct fuse_args_pages *ap = container_of(args, typeof(*ap), args); - unsigned int total_sgs = 1 /* fuse_in_header */; + unsigned int size, total_sgs = 1 /* fuse_in_header */; if (args->in_numargs - args->in_pages) total_sgs += 1; - if (args->in_pages) - total_sgs += ap->num_pages; + if (args->in_pages) { + size = args->in_args[args->in_numargs - 1].size; + total_sgs += sg_count_fuse_pages(ap->descs, ap->num_pages, + size); + } if (!test_bit(FR_ISREPLY, &req->flags)) return total_sgs; @@ -1054,8 +1073,11 @@ static unsigned int sg_count_fuse_req(struct fuse_req *req) if (args->out_numargs - args->out_pages) total_sgs += 1; - if (args->out_pages) - total_sgs += ap->num_pages; + if (args->out_pages) { + size = args->out_args[args->out_numargs - 1].size; + total_sgs += sg_count_fuse_pages(ap->descs, ap->num_pages, + size); + } return total_sgs; }