On Fri, Oct 16, 2020 at 02:40:09PM +0200, Peter Zijlstra wrote:
> On Fri, Oct 16, 2020 at 11:21:47AM +0500, Mikhail Gavrilov wrote:
> > Hi folks,
> > today I joined to testing Kernel 5.10 and see that every boot happens
> > this warning:
> >
> > [ 9.032096] ======================================================
> > [ 9.032097] WARNING: possible circular locking dependency detected
> > [ 9.032098] 5.10.0-0.rc0.20201014gitb5fc7a89e58b.41.fc34.x86_64 #1 Not tainted
> > [ 9.032099] ------------------------------------------------------
> > [ 9.032100] swapon/913 is trying to acquire lock:
> > [ 9.032101] ffffc984fda4f948 (&zstrm->lock){+.+.}-{2:2}, at: zcomp_stream_get+0x5/0x90 [zram]
> > [ 9.032106] but task is already holding lock:
> > [ 9.032107] ffff993c54cdceb0 (&zspage->lock){.+.+}-{2:2}, at: zs_map_object+0x7a/0x2e0
> > [ 9.032111] which lock already depends on the new lock.
> > [ 9.032112] the existing dependency chain (in reverse order) is:
>
> > [ 9.032112] -> #1 (&zspage->lock){.+.+}-{2:2}:
> > [ 9.032116] _raw_read_lock+0x3d/0xa0
> > [ 9.032118] zs_map_object+0x7a/0x2e0
> > [ 9.032119] zram_bvec_rw.constprop.0.isra.0+0x287/0x730 [zram]
> > [ 9.032121] zram_submit_bio+0x189/0x35d [zram]
> > [ 9.032123] submit_bio_noacct+0xff/0x650
> > [ 9.032124] submit_bh_wbc+0x17d/0x1a0
> > [ 9.032126] __block_write_full_page+0x227/0x580
> > [ 9.032128] __writepage+0x1a/0x70
> > [ 9.032129] write_cache_pages+0x21c/0x540
> > [ 9.032130] generic_writepages+0x41/0x60
> > [ 9.032131] do_writepages+0x28/0xb0
> > [ 9.032133] __filemap_fdatawrite_range+0xa7/0xe0
> > [ 9.032134] file_write_and_wait_range+0x67/0xb0
> > [ 9.032135] blkdev_fsync+0x17/0x40
> > [ 9.032137] __x64_sys_fsync+0x34/0x60
> > [ 9.032138] do_syscall_64+0x33/0x40
> > [ 9.032140] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > [ 9.032140]
> > -> #0 (&zstrm->lock){+.+.}-{2:2}:
>
>
> > [ 9.032169] 1 lock held by swapon/913:
> > [ 9.032170] #0: ffff993c54cdceb0 (&zspage->lock){.+.+}-{2:2}, at: zs_map_object+0x7a/0x2e0
>
> > [ 9.032176] Call Trace:
> > [ 9.032179] dump_stack+0x8b/0xb0
> > [ 9.032181] check_noncircular+0xd0/0xf0
> > [ 9.032183] __lock_acquire+0x11e3/0x21f0
> > [ 9.032185] lock_acquire+0xc8/0x400
> > [ 9.032187] ? zcomp_stream_get+0x5/0x90 [zram]
> > [ 9.032189] zcomp_stream_get+0x38/0x90 [zram]
> > [ 9.032190] ? zcomp_stream_get+0x5/0x90 [zram]
> > [ 9.032192] zram_bvec_rw.constprop.0.isra.0+0x4c1/0x730 [zram]
> > [ 9.032194] ? __part_start_io_acct+0x4d/0xf0
> > [ 9.032196] zram_rw_page+0xa9/0x130 [zram]
> > [ 9.032197] bdev_read_page+0x71/0xa0
> > [ 9.032199] do_mpage_readpage+0x5a8/0x800
> > [ 9.032201] ? xa_load+0xbf/0x140
> > [ 9.032203] mpage_readahead+0xfb/0x230
> > [ 9.032205] ? bdev_evict_inode+0x1a0/0x1a0
> > [ 9.032207] read_pages+0x60/0x1e0
> > [ 9.032208] page_cache_readahead_unbounded+0x1da/0x270
> > [ 9.032211] generic_file_buffered_read+0x69c/0xe00
> > [ 9.032213] new_sync_read+0x108/0x180
> > [ 9.032215] vfs_read+0x12e/0x1c0
> > [ 9.032217] ksys_read+0x58/0xd0
> > [ 9.032218] do_syscall_64+0x33/0x40
> > [ 9.032219] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
>
> Joy... __zram_bvec_write() and __zram_bvec_read() take these locks in
> opposite order.
>
> Does something like the (_completely_) untested below cure things?
[19f545b6e07f7, zram: Use local lock to protect per-CPU data] introduced
new lock dependency and this patch looks good to me.
Peter, do you mind sending this patch with fix tag to Andrew Morton?
Thanks for your help.
>
> ---
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 9100ac36670a..c1e2c2e1cde8 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1216,10 +1216,11 @@ static void zram_free_page(struct zram *zram, size_t index)
> static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
> struct bio *bio, bool partial_io)
> {
> - int ret;
> + struct zcomp_strm *zstrm;
> unsigned long handle;
> unsigned int size;
> void *src, *dst;
> + int ret;
>
> zram_slot_lock(zram, index);
> if (zram_test_flag(zram, index, ZRAM_WB)) {
> @@ -1250,6 +1251,9 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
>
> size = zram_get_obj_size(zram, index);
>
> + if (size != PAGE_SIZE)
> + zstrm = zcomp_stream_get(zram->comp);
> +
> src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
> if (size == PAGE_SIZE) {
> dst = kmap_atomic(page);
> @@ -1257,8 +1261,6 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
> kunmap_atomic(dst);
> ret = 0;
> } else {
> - struct zcomp_strm *zstrm = zcomp_stream_get(zram->comp);
> -
> dst = kmap_atomic(page);
> ret = zcomp_decompress(zstrm, src, size, dst);
> kunmap_atomic(dst);
