From 2b269ce6fcbfafc6cae37254cab4bf2309bfed0e Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Thu, 12 Feb 2015 15:00:42 -0800 Subject: [PATCH] zram: check bd_openers instead of bd_holders bd_holders is increased only when user open the device file as FMODE_EXCL so if something opens zram0 as !FMODE_EXCL and request I/O while another user reset zram0, we can see following warning. zram0: detected capacity change from 0 to 64424509440 Buffer I/O error on dev zram0, logical block 180823, lost async page write Buffer I/O error on dev zram0, logical block 180824, lost async page write Buffer I/O error on dev zram0, logical block 180825, lost async page write Buffer I/O error on dev zram0, logical block 180826, lost async page write Buffer I/O error on dev zram0, logical block 180827, lost async page write Buffer I/O error on dev zram0, logical block 180828, lost async page write Buffer I/O error on dev zram0, logical block 180829, lost async page write Buffer I/O error on dev zram0, logical block 180830, lost async page write Buffer I/O error on dev zram0, logical block 180831, lost async page write Buffer I/O error on dev zram0, logical block 180832, lost async page write ------------[ cut here ]------------ WARNING: CPU: 11 PID: 1996 at fs/block_dev.c:57 __blkdev_put+0x1d7/0x210() Modules linked in: CPU: 11 PID: 1996 Comm: dd Not tainted 3.19.0-rc6-next-20150202+ #1125 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: dump_stack+0x45/0x57 warn_slowpath_common+0x8a/0xc0 warn_slowpath_null+0x1a/0x20 __blkdev_put+0x1d7/0x210 blkdev_put+0x50/0x130 blkdev_close+0x25/0x30 __fput+0xdf/0x1e0 ____fput+0xe/0x10 task_work_run+0xa7/0xe0 do_notify_resume+0x49/0x60 int_signal+0x12/0x17 ---[ end trace 274fbbc5664827d2 ]--- The warning comes from bdev_write_node in blkdev_put path. static void bdev_write_inode(struct inode *inode) { spin_lock(&inode->i_lock); while (inode->i_state & I_DIRTY) { spin_unlock(&inode->i_lock); WARN_ON_ONCE(write_inode_now(inode, true)); <========= here. spin_lock(&inode->i_lock); } spin_unlock(&inode->i_lock); } The reason is dd process encounters I/O fails due to sudden block device disappear so in filemap_check_errors in __writeback_single_inode returns -EIO. If we check bd_openers instead of bd_holders, we could address the problem. When I see the brd, it already have used it rather than bd_holders so although I'm not a expert of block layer, it seems to be better. I can make following warning with below simple script. In addition, I added msleep(2000) below set_capacity(zram->disk, 0) after applying your patch to make window huge(Kudos to Ganesh!) script: echo $((60<<30)) > /sys/block/zram0/disksize setsid dd if=/dev/zero of=/dev/zram0 & sleep 1 setsid echo 1 > /sys/block/zram0/reset Signed-off-by: Minchan Kim Acked-by: Sergey Senozhatsky Cc: Nitin Gupta Cc: Jerome Marchand Cc: Ganesh Mahendran Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/block/zram/zram_drv.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 81ac8fd53340..0abcf4a31c78 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -810,7 +810,7 @@ static ssize_t reset_store(struct device *dev, mutex_lock(&bdev->bd_mutex); /* Do not reset an active device! */ - if (bdev->bd_holders) { + if (bdev->bd_openers) { ret = -EBUSY; goto out; } -- GitLab