Re: [PATCH] zram: make rw_page opeartion return 0

[Sergey Senozhatsky]

Hello,

On (11/05/14 09:10), Minchan Kim wrote:
> zram_rw_page returns error code to upper layer with PG_error flag
> of the page but it should be wrong usage. If submitted IO is
> hard fail(ie, I/O again will not succeed), we should return 0,
> indicating that the submission was successful but the IO operation
> failed.
> 
> http://marc.info/?l=linux-mm&m=141511693112734&w=2
> 

well, `don't return error in case of an error' is a bit misleading.

apart from zram there seems to be one block driver that does the
same: brd.c [git grep page_endio]. so I Cc Nick Piggin.

> This patch fixes below BUG.
> 
> [  179.987592] zram0: detected capacity change from 2147483648 to 0
> [  179.987570] page:ffffea00008d6300 count:2 mapcount:0 mapping:ffff880025348e88 index:0x0
> [  179.987570] flags: 0x100000000020002(error|mappedtodisk)
> [  179.987570] page dumped because: VM_BUG_ON_PAGE(!PageLocked(page))
> [  179.987570] ------------[ cut here ]------------
> [  179.987570] kernel BUG at mm/filemap.c:747!
> [  179.987570] invalid opcode: 0000 [#1] SMP
> [  179.987570] Dumping ftrace buffer:
> [  179.987570]    (ftrace buffer empty)
> [  179.987570] Modules linked in:
> [  179.987570] CPU: 10 PID: 23080 Comm: udisks-part-id Not tainted 3.18.0-rc2+ #584
> [  179.987570] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> [  179.987570] task: ffff88001de74200 ti: ffff88001b220000 task.ti: ffff88001b220000
> [  179.987570] RIP: 0010:[<ffffffff8114ae12>]  [<ffffffff8114ae12>] unlock_page+0x82/0x90
> [  179.987570] RSP: 0018:ffff88001b223998  EFLAGS: 00010246
> [  179.987570] RAX: 0000000000000036 RBX: ffff88001e009a50 RCX: 000000000910090f
> [  179.987570] RDX: 0000000000000910 RSI: 0000000000000001 RDI: ffffffff81600a7f
> [  179.987570] RBP: ffff88001b223998 R08: 0000000000000001 R09: 0000000000000001
> [  179.987570] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000001
> [  179.987570] R13: ffff88001e0099c0 R14: 00000000fffffffb R15: ffff88001e0099c0
> [  179.987570] FS:  00007fcb17c73800(0000) GS:ffff880027f40000(0000) knlGS:0000000000000000
> [  179.987570] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [  179.987570] CR2: 00007fff1629ebc8 CR3: 000000001dc4f000 CR4: 00000000000006e0
> [  179.987570] Stack:
> [  179.987570]  ffff88001b2239a8 ffffffff8114afde ffff88001b2239d8 ffffffff811f2e52
> [  179.987570]  ffff88001e0099c0 00000000fffffffb 0000000000000000 ffff880025348e88
> [  179.987570]  ffff88001b223a08 ffffffff812e9ad3 ffff88001b223a08 ffffffff8109b6b3
> [  179.987570] Call Trace:
> [  179.987570]  [<ffffffff8114afde>] page_endio+0x1e/0x80
> [  179.987570]  [<ffffffff811f2e52>] mpage_end_io+0x42/0x60
> [  179.987570]  [<ffffffff812e9ad3>] bio_endio+0x53/0xa0
> [  179.987570]  [<ffffffff8109b6b3>] ? up_read+0x23/0x40
> [  179.987570]  [<ffffffff81413f09>] zram_make_request+0x2a9/0x3c0
> [  179.987570]  [<ffffffff812ee330>] generic_make_request+0xc0/0x100
> [  179.987570]  [<ffffffff812ee3e5>] submit_bio+0x75/0x140
> [  179.987570]  [<ffffffff812ee375>] ? submit_bio+0x5/0x140
> [  179.987570]  [<ffffffff811f2e03>] mpage_bio_submit+0x33/0x40
> [  179.987570]  [<ffffffff811f3de5>] mpage_readpages+0xf5/0x110
> [  179.987570]  [<ffffffff811ed7a0>] ? I_BDEV+0x10/0x10
> [  179.987570]  [<ffffffff811ed7a0>] ? I_BDEV+0x10/0x10
> [  179.987570]  [<ffffffff81603241>] ? ftrace_call+0x5/0x2f
> [  179.987570]  [<ffffffff81603241>] ? ftrace_call+0x5/0x2f
> [  179.987570]  [<ffffffff811ee190>] ? blkdev_write_begin+0x30/0x30
> [  179.987570]  [<ffffffff811ed7a0>] ? I_BDEV+0x10/0x10
> [  179.987570]  [<ffffffff811ee1ad>] blkdev_readpages+0x1d/0x20
> [  179.987570]  [<ffffffff81158ed4>] __do_page_cache_readahead+0x204/0x290
> [  179.987570]  [<ffffffff81158d99>] ? __do_page_cache_readahead+0xc9/0x290
> [  179.987570]  [<ffffffff8114b045>] ? find_get_entry+0x5/0x130
> [  179.987570]  [<ffffffff811593cd>] force_page_cache_readahead+0x7d/0xb0
> [  179.987570]  [<ffffffff81159443>] page_cache_sync_readahead+0x43/0x50
> [  179.987570]  [<ffffffff8114d0e1>] generic_file_read_iter+0x451/0x650
> [  179.987570]  [<ffffffff81603241>] ? ftrace_call+0x5/0x2f
> [  179.987570]  [<ffffffff811ed947>] blkdev_read_iter+0x37/0x40
> [  179.987570]  [<ffffffff811b4358>] new_sync_read+0x78/0xb0
> [  179.987570]  [<ffffffff811b555b>] vfs_read+0xab/0x180
> [  179.987570]  [<ffffffff811b5682>] SyS_read+0x52/0xb0
> [  179.987570]  [<ffffffff816011d2>] system_call_fastpath+0x12/0x17
> [  179.987570] Code: 00 4c 8b 82 f8 00 00 00 31 d2 48 d3 ee 48 8d 3c f6 48 89 c6 49 8d 3c f8 e8 dc 9f f4 ff 5d c3 48 c7 c6 88 2c a0 81 e8 1e a8 02 00 <0f> 0b 66 66 66 2e 0f 1f 84 00 00 00 00 00 e8 bb 83 4b 00 55 48
> [  179.987570] RIP  [<ffffffff8114ae12>] unlock_page+0x82/0x90
> [  179.987570]  RSP <ffff88001b223998>
> [  179.987570] ---[ end trace 39c73c1d9da87ec4 ]---
> [  180.030327] zram0: detected capacity change from 0 to 2147483648
> [  180.033795] Adding 2097148k swap on /dev/zram0.  Priority:-1 extents:1 across:2097148k SSFS
> [  181.978291] zram_kern_compi (2685): drop_caches: 3
> 
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
> Cc: Dave Chinner <david@xxxxxxxxxxxxx>
> Cc: Karam Lee <karam.lee@xxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
>  drivers/block/zram/zram_drv.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 05e8e54551de..004d758f0c39 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -947,7 +947,7 @@ static void zram_slot_free_notify(struct block_device *bdev,
>  static int zram_rw_page(struct block_device *bdev, sector_t sector,
>  		       struct page *page, int rw)
>  {
> -	int offset, ret;
> +	int offset, err;
>  	u32 index;
>  	struct zram *zram;
>  	struct bio_vec bv;
> @@ -955,13 +955,13 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
>  	zram = bdev->bd_disk->private_data;
>  	if (!valid_io_request(zram, sector, PAGE_SIZE)) {
>  		atomic64_inc(&zram->stats.invalid_io);
> -		ret = -EINVAL;
> +		err = -EINVAL;
>  		goto out;
>  	}
>  
>  	down_read(&zram->init_lock);
>  	if (unlikely(!init_done(zram))) {
> -		ret = -EIO;
> +		err = -EIO;
>  		goto out_unlock;
>  	}
>  
> @@ -972,13 +972,18 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
>  	bv.bv_len = PAGE_SIZE;
>  	bv.bv_offset = 0;
>  
> -	ret = zram_bvec_rw(zram, &bv, index, offset, rw);
> +	err = zram_bvec_rw(zram, &bv, index, offset, rw);
>  
>  out_unlock:
>  	up_read(&zram->init_lock);
>  out:
> -	page_endio(page, rw, ret);
> -	return ret;
> +	page_endio(page, rw, err);
> +
> +	/*
> +	 * Return 0 prevents I/O fallback trial caused by rw_page fail
> +	 * and upper layer can handle this IO error via page error.
> +	 */
> +	return 0;


so, the patch is a one-liner. is there any reason to rename `err' to `ret'?

	-ss

>  }
>  
>  static const struct block_device_operations zram_devops = {
> -- 
> 2.0.0
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/