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Date: Tue, 3 Feb 2015 13:50:46 +0900
From: Minchan Kim <minchan@...nel.org>
To: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>, Nitin Gupta <ngupta@...are.org>,
Jerome Marchand <jmarchan@...hat.com>,
Ganesh Mahendran <opensource.ganesh@...il.com>
Subject: [PATCH] zram: check bd_openers instead bd_holders
On Tue, Feb 03, 2015 at 12:56:28PM +0900, Sergey Senozhatsky wrote:
> On (02/03/15 12:02), Minchan Kim wrote:
> > On Tue, Feb 03, 2015 at 10:54:33AM +0900, Sergey Senozhatsky wrote:
> > > On (02/02/15 16:06), Sergey Senozhatsky wrote:
> > > > So, guys, how about doing it differently, in less lines of code,
> > > > hopefully. Don't move reset_store()'s work to zram_reset_device().
> > > > Instead, move
> > > >
> > > > set_capacity(zram->disk, 0);
> > > > revalidate_disk(zram->disk);
> > > >
> > > > out from zram_reset_device() to reset_store(). this two function are
> > > > executed only when called from reset_store() anyway. this also will let
> > > > us drop `bool reset capacity' param from zram_reset_device().
> > > >
> > > >
> > > > so we will do in reset_store()
> > > >
> > > > mutex_lock(bdev->bd_mutex);
> > > >
> > > > fsync_bdev(bdev);
> > > > zram_reset_device(zram);
> > > > set_capacity(zram->disk, 0);
> > > >
> > > > mutex_unlock(&bdev->bd_mutex);
> > > >
> > > > revalidate_disk(zram->disk);
> > > > bdput(bdev);
> > > >
> > > >
> > > >
> > > > and change zram_reset_device(zram, false) call to simply zram_reset_device(zram)
> > > > in __exit zram_exit(void).
> > > >
> > >
> > > Hello,
> > >
> > > Minchan, Ganesh, I sent a patch last night, with the above solution.
> > > looks ok to you?
> >
> > Just I sent a feedback.
> >
>
> thanks.
> yeah, !FMODE_EXCL mode.
>
> how do you want to handle it -- you want to send a separate patch or
> you want me to send incremental one-liner and ask Andrew to squash them?
Send a new patch based on yours.
Thanks.
>From 9da15eb638ba74d8072a1e2451c5036e8473f03a Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@...nel.org>
Date: Tue, 3 Feb 2015 13:42:35 +0900
Subject: [PATCH] zram: check bd_openers instead bd_holders
The 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.
[ 30.683449] zram0: detected capacity change from 0 to 64424509440
[ 33.736869] Buffer I/O error on dev zram0, logical block 180823, lost async page write
[ 33.738814] Buffer I/O error on dev zram0, logical block 180824, lost async page write
[ 33.740654] Buffer I/O error on dev zram0, logical block 180825, lost async page write
[ 33.742551] Buffer I/O error on dev zram0, logical block 180826, lost async page write
[ 33.744153] Buffer I/O error on dev zram0, logical block 180827, lost async page write
[ 33.745807] Buffer I/O error on dev zram0, logical block 180828, lost async page write
[ 33.747419] Buffer I/O error on dev zram0, logical block 180829, lost async page write
[ 33.749060] Buffer I/O error on dev zram0, logical block 180830, lost async page write
[ 33.750687] Buffer I/O error on dev zram0, logical block 180831, lost async page write
[ 33.752286] Buffer I/O error on dev zram0, logical block 180832, lost async page write
[ 33.811590] ------------[ cut here ]------------
[ 33.812038] WARNING: CPU: 11 PID: 1996 at fs/block_dev.c:57 __blkdev_put+0x1d7/0x210()
[ 33.812817] Modules linked in:
[ 33.813142] CPU: 11 PID: 1996 Comm: dd Not tainted 3.19.0-rc6-next-20150202+ #1125
[ 33.813837] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
[ 33.814525] ffffffff81801a2d ffff880061e77db8 ffffffff815b848e 0000000000000001
[ 33.815196] 0000000000000000 ffff880061e77df8 ffffffff8104de2a 0000000000000000
[ 33.815867] ffff88005da287f0 ffff88005da28680 ffff88005da28770 ffff88005da28698
[ 33.816536] Call Trace:
[ 33.816817] [<ffffffff815b848e>] dump_stack+0x45/0x57
[ 33.817304] [<ffffffff8104de2a>] warn_slowpath_common+0x8a/0xc0
[ 33.817829] [<ffffffff8104df1a>] warn_slowpath_null+0x1a/0x20
[ 33.818331] [<ffffffff811b60b7>] __blkdev_put+0x1d7/0x210
[ 33.818797] [<ffffffff811b69c0>] blkdev_put+0x50/0x130
[ 33.819244] [<ffffffff811b6b55>] blkdev_close+0x25/0x30
[ 33.819723] [<ffffffff8118079f>] __fput+0xdf/0x1e0
[ 33.820140] [<ffffffff811808ee>] ____fput+0xe/0x10
[ 33.820576] [<ffffffff81068e07>] task_work_run+0xa7/0xe0
[ 33.821151] [<ffffffff81002b89>] do_notify_resume+0x49/0x60
[ 33.821721] [<ffffffff815bf09d>] int_signal+0x12/0x17
[ 33.822228] ---[ end trace 274fbbc5664827d2 ]---
The warning comes from bdev_write_node in blkdev_put path.
tatic 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 checks bd_openners 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
If we checks bd_openners 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.
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
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 a32069f98afa..cc0e6a3ddb4f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -811,7 +811,7 @@ 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;
}
--
1.9.1
--
Kind regards,
Minchan Kim
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