On Mon, Aug 10, 2020 at 6:09 AM David Howells <dhowells@xxxxxxxxxx> wrote:
>
> David Wysochanski <dwysocha@xxxxxxxxxx> wrote:
>
> > Looks like fscache_shape_request() overrides any 'max_pages' value (actually
> > it is cachefiles_shape_request) , so it's unclear why the netfs would pass
> > in a 'max_pages' if it is not honored - seems like a bug maybe or it's not
> > obvious
>
> I think the problem is that cachefiles_shape_request() is applying the limit
> too early. It's using it to cut down the number of pages in the original
> request (only applicable to readpages), but then the shaping to fit cache
> granules can exceed that, so it needs to be applied later also.
>
> Does the attached patch help?
>
> David
> ---
> diff --git a/fs/cachefiles/content-map.c b/fs/cachefiles/content-map.c
> index 2bfba2e41c39..ce05cf1d9a6e 100644
> --- a/fs/cachefiles/content-map.c
> +++ b/fs/cachefiles/content-map.c
> @@ -134,7 +134,8 @@ void cachefiles_shape_request(struct fscache_object *obj,
> _enter("{%lx,%lx,%x},%llx,%d",
> start, end, max_pages, i_size, shape->for_write);
>
> - if (start >= CACHEFILES_SIZE_LIMIT / PAGE_SIZE) {
> + if (start >= CACHEFILES_SIZE_LIMIT / PAGE_SIZE ||
> + max_pages < CACHEFILES_GRAN_PAGES) {
> shape->to_be_done = FSCACHE_READ_FROM_SERVER;
> return;
> }
> @@ -144,10 +145,6 @@ void cachefiles_shape_request(struct fscache_object *obj,
> if (shape->i_size > CACHEFILES_SIZE_LIMIT)
> i_size = CACHEFILES_SIZE_LIMIT;
>
> - max_pages = round_down(max_pages, CACHEFILES_GRAN_PAGES);
> - if (end - start > max_pages)
> - end = start + max_pages;
> -
> granule = start / CACHEFILES_GRAN_PAGES;
> if (granule / 8 >= object->content_map_size) {
> cachefiles_expand_content_map(object, i_size);
> @@ -185,6 +182,10 @@ void cachefiles_shape_request(struct fscache_object *obj,
> start = round_down(start, CACHEFILES_GRAN_PAGES);
> end = round_up(end, CACHEFILES_GRAN_PAGES);
>
> + /* Trim to the maximum size the netfs supports */
> + if (end - start > max_pages)
> + end = round_down(start + max_pages, CACHEFILES_GRAN_PAGES);
> +
> /* But trim to the end of the file and the starting page */
> eof = (i_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
> if (eof <= shape->proposed_start)
>
I tried this and got the same panic - I think i_size is the culprit
(it is larger than max_pages). I'll send you a larger trace offline
with cachefiles/fscache debugging enabled if that helps, but below is
some custom tracing that may be enough because it shows before / after
shaping values.
Here's outline of the test (smaller rsize and readahead for simplicity):
# ./t1_rsize_lt_read.sh 4.1
Setting NFS vers=4.1
Mon 10 Aug 2020 09:34:18 AM EDT: 1. On NFS client, install and enable
cachefilesd
Mon 10 Aug 2020 09:34:18 AM EDT: 2. On NFS client, mount -o
vers=4.1,fsc,rsize=8192 127.0.0.1:/export/dir1 /mnt/dir1
Mon 10 Aug 2020 09:34:18 AM EDT: 3. On NFS client, dd if=/dev/zero
of=/mnt/dir1/file1.bin bs=16384 count=1
Mon 10 Aug 2020 09:34:18 AM EDT: 4. On NFS client, echo 3 >
/proc/sys/vm/drop_caches
Mon 10 Aug 2020 09:34:19 AM EDT: 5. On NFS client, ./nfs-readahead.sh
set /mnt/dir1 16384
Mon 10 Aug 2020 09:34:19 AM EDT: 6. On NFS client, dd
if=/mnt/dir1/file1.bin of=/dev/null
Mon 10 Aug 2020 09:34:19 AM EDT: 7. On NFS client, echo 3 >
/proc/sys/vm/drop_caches
Mon 10 Aug 2020 09:34:19 AM EDT: 8. On NFS client, dd
if=/mnt/dir1/file1.bin of=/dev/null
Console with custom nfs tracing
[ 62.955355] t1_rsize_lt_rea (4840): drop_caches: 3
[ 63.028786] fs/nfs/fscache.c:480 before read_helper_page_list pid
4882 inode ffff8902b4a2a828 cache ffff8902f50b5800 pages
ffffb4b4c0fafca8 max_pages 2
[ 63.028804] fs/fscache/read_helper.c:347 pid 4882
fscache_read_helper before shape req ffff8902f50b5800 req->nr_pages 0
shape.actual_nr_pages 48 shape.proposed_nr_pages 4
[ 63.037231] fs/fscache/read_helper.c:353 pid 4882
fscache_read_helper after shape req ffff8902f50b5800 req->nr_pages 0
shape.actual_nr_pages 4 shape.proposed_nr_pages 4
[ 63.043421] fs/fscache/read_helper.c:531 pid 4882
fscache_read_helper before while req ffff8902f50b5800 req->nr_pages 1
shape.actual_nr_pages 4 shape.proposed_nr_pages 4
[ 63.049498] fs/fscache/read_helper.c:531 pid 4882
fscache_read_helper before while req ffff8902f50b5800 req->nr_pages 2
shape.actual_nr_pages 4 shape.proposed_nr_pages 4
[ 63.063708] fs/fscache/read_helper.c:531 pid 4882
fscache_read_helper before while req ffff8902f50b5800 req->nr_pages 3
shape.actual_nr_pages 4 shape.proposed_nr_pages 4
[ 63.070114] fs/fscache/read_helper.c:531 pid 4882
fscache_read_helper before while req ffff8902f50b5800 req->nr_pages 4
shape.actual_nr_pages 4 shape.proposed_nr_pages 4
[ 63.076438] fs/nfs/fscache.c:369 enter nfs_issue_op pid 4882 inode
ffff8902b4a2a828 cache ffff8902f50b5800 start 0 last 3
[ 63.082964] fs/nfs/fscache.c:379 before readpage_async_filler pid
4882 inode ffff8902b4a2a828 cache ffff8902f50b5800 page
fffff42f08741a00
[ 63.087591] fs/nfs/fscache.c:382 after readpage_async_filler pid
4882 inode ffff8902b4a2a828 cache ffff8902f50b5800 page
fffff42f08741a00 cache.error 0
[ 63.093058] fs/nfs/fscache.c:379 before readpage_async_filler pid
4882 inode ffff8902b4a2a828 cache ffff8902f50b5800 page
fffff42f08288680
[ 63.098927] fs/nfs/fscache.c:382 after readpage_async_filler pid
4882 inode ffff8902b4a2a828 cache ffff8902f50b5800 page
fffff42f08288680 cache.error 0
[ 63.104507] fs/nfs/fscache.c:379 before readpage_async_filler pid
4882 inode ffff8902b4a2a828 cache ffff8902f50b5800 page
fffff42f082816c0
[ 63.110922] fs/nfs/fscache.c:382 after readpage_async_filler pid
4882 inode ffff8902b4a2a828 cache ffff8902f50b5800 page
fffff42f082816c0 cache.error 0
[ 63.111973] fs/nfs/fscache.c:523 pid 233 before io_done inode
ffff8902b4a2a828 bytes 8192 &req->cache ffff8902f50b5800 cache.pos 0
cache.len 16384
[ 63.115407] fs/nfs/fscache.c:379 before readpage_async_filler pid
4882 inode ffff8902b4a2a828 cache ffff8902f50b5800 page
fffff42f067e8f40
[ 63.126337] fs/nfs/fscache.c:382 after readpage_async_filler pid
4882 inode ffff8902b4a2a828 cache ffff8902f50b5800 page
fffff42f067e8f40 cache.error 0
[ 63.131411] fs/nfs/fscache.c:388 exit nfs_issue_op pid 4882 inode
ffff8902b4a2a828 cache ffff8902f50b5800
[ 63.131955] fs/nfs/fscache.c:523 pid 233 before io_done inode
ffff8902b4a2a828 bytes 8192 &req->cache ffff8902f50b5800 cache.pos 0
cache.len 16384
[ 63.137012] fs/nfs/fscache.c:484 after read_helper_page_list pid
4882 inode ffff8902b4a2a828 cache ffff8902f50b5800 cache.pos 0
cache.len 16384 cache.nr_pages 4 pages ffffb4b4c0fafca8 ret 0
[ 63.140922] page:fffff42f08741a00 refcount:2 mapcount:0
mapping:00000000727f3adc index:0x0
[ 63.141091] mapping->aops:nfs_file_aops [nfs] dentry name:"file1.bin"
[ 63.146475] fs/nfs/fscache.c:490 outside while(!list_empty(pages))
read_helper_page_list pid 4882 inode ffff8902b4a2a828 cache
ffff8902f50b5800 cache.pos 0 cache.len 16384 cache.nr_pages 4
[ 63.146740] fs/fscache/read_helper.c:347 pid 4882
fscache_read_helper before shape req ffff8902f50b5800 req->nr_pages 0
shape.actual_nr_pages 3227832042 shape.proposed_nr_pages 1
[ 63.153662] flags: 0x17ffffc0000006(referenced|uptodate)
[ 63.153699] raw: 0017ffffc0000006 dead000000000100 dead000000000122
ffff8902b4a2a9a0
[ 63.168174] fs/fscache/read_helper.c:353 pid 4882
fscache_read_helper after shape req ffff8902f50b5800 req->nr_pages 0
shape.actual_nr_pages 5 shape.proposed_nr_pages 1
[ 63.193131] raw: 0000000000000000 0000000000000000 00000001ffffffff
ffff8902ecfe8000
[ 63.203785] page dumped because: VM_BUG_ON_PAGE(!PageLocked(page))
[ 63.206372] page->mem_cgroup:ffff8902ecfe8000
[ 63.208333] ------------[ cut here ]------------
[ 63.211081] kernel BUG at mm/filemap.c:1290!
[ 63.213152] invalid opcode: 0000 [#1] SMP PTI
