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SubjectRe: [PATCH] zram: revalidate disk after capacity change
On (07/04/14 09:44), Minchan Kim wrote:
> Hello Sasha,
>
> On Thu, Jul 03, 2014 at 04:39:48PM -0400, Sasha Levin wrote:
> > On 06/25/2014 09:16 PM, Minchan Kim wrote:
> > > Alexander reported mkswap on /dev/zram0 is failed if other process
> > > is opening the block device file.
> > >
> > > Step is as follows,
> > >
> > > 0. Reset the unused zram device.
> > > 1. Use a program that opens /dev/zram0 with O_RDWR and sleeps
> > > until killed.
> > > 2. While that program sleeps, echo the correct value to
> > > /sys/block/zram0/disksize.
> > > 3. Verify (e.g. in /proc/partitions) that the disk size is applied
> > > correctly. It is.
> > > 4. While that program still sleeps, attempt to mkswap /dev/zram0.
> > > This fails: mkswap: error: swap area needs to be at least 40 KiB
> > >
> > > When I investigated, the size get by ioctl(fd, BLKGETSIZE64, xxx)
> > > on mkswap to get a size of blockdev was zero although zram0 has
> > > right size by 2.
> > >
> > > The reason is zram didn't revalidate disk after changing capacity
> > > so that size of blockdev's inode is not uptodate until all of file
> > > is close.
> > >
> > > This patch should fix the BUG.
> > >
> > > Cc: stable@vger.kernel.org
> > > Reported-and-Tested-by: Alexander E. Patrakov <patrakov@gmail.com>
> > > Signed-off-by: Minchan Kim <minchan@kernel.org>
> >
> > Hi Minchan,
> >
> > This patch causes the following lockdep warning:
> >
> >
> > [ 249.545546] =================================
> > [ 249.546510] [ INFO: inconsistent lock state ]
> > [ 249.547201] 3.16.0-rc3-next-20140703-sasha-00022-g0b37949-dirty #761 Not tainted
> > [ 249.548316] ---------------------------------
> > [ 249.548980] inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-R} usage.
> > [ 249.550044] kswapd1/3912 [HC0[0]:SC0[0]:HE1:SE1] takes:
> > [ 249.550044] (&zram->init_lock){+++++-}, at: zram_make_request (drivers/block/zram/zram_drv.c:1047)
> > [ 249.550044] {RECLAIM_FS-ON-W} state was registered at:
> > [ 249.550044] mark_held_locks (kernel/locking/lockdep.c:2523)
> > [ 249.550044] lockdep_trace_alloc (kernel/locking/lockdep.c:2745 kernel/locking/lockdep.c:2760)
> > [ 249.550044] kmem_cache_alloc (mm/slub.c:1246 mm/slub.c:2386 mm/slub.c:2459 mm/slub.c:2464)
> > [ 249.550044] bdev_alloc_inode (fs/block_dev.c:440)
> > [ 249.550044] alloc_inode (fs/inode.c:208)
> > [ 249.550044] iget5_locked (fs/inode.c:1017)
> > [ 249.550044] bdget (fs/block_dev.c:568)
> > [ 249.550044] bdget_disk (include/linux/genhd.h:268 block/genhd.c:727)
> > [ 249.550044] revalidate_disk (fs/block_dev.c:1042)
> > [ 249.550044] disksize_store (drivers/block/zram/zram_drv.c:685)
> > [ 249.550044] dev_attr_store (drivers/base/core.c:138)
> > [ 249.550044] sysfs_kf_write (fs/sysfs/file.c:115)
> > [ 249.550044] kernfs_fop_write (fs/kernfs/file.c:308)
> > [ 249.550044] vfs_write (fs/read_write.c:532)
> > [ 249.550044] SyS_write (fs/read_write.c:584 fs/read_write.c:576)
> > [ 249.550044] tracesys (arch/x86/kernel/entry_64.S:542)
> > [ 249.550044] irq event stamp: 4395
> > [ 249.550044] hardirqs last enabled at (4395): throtl_update_dispatch_stats (./arch/x86/include/asm/paravirt.h:809 (discriminator 2) block/blk-throttle.c:982 (discriminator 2))
> > [ 249.550044] hardirqs last disabled at (4394): throtl_update_dispatch_stats (block/blk-throttle.c:977)
> > [ 249.550044] softirqs last enabled at (4252): __do_softirq (./arch/x86/include/asm/preempt.h:22 kernel/softirq.c:296)
> > [ 249.550044] softirqs last disabled at (4233): irq_exit (kernel/softirq.c:346 kernel/softirq.c:387)
> > [ 249.550044]
> > [ 249.550044] other info that might help us debug this:
> > [ 249.550044] Possible unsafe locking scenario:
> > [ 249.550044]
> > [ 249.550044] CPU0
> > [ 249.550044] ----
> > [ 249.550044] lock(&zram->init_lock);
> > [ 249.550044] <Interrupt>
> > [ 249.550044] lock(&zram->init_lock);
> > [ 249.550044]
> > [ 249.550044] *** DEADLOCK ***
> > [ 249.550044]
> > [ 249.550044] no locks held by kswapd1/3912.
> > [ 249.550044]
> > [ 249.550044] stack backtrace:
> > [ 249.550044] CPU: 1 PID: 3912 Comm: kswapd1 Not tainted 3.16.0-rc3-next-20140703-sasha-00022-g0b37949-dirty #761
> > [ 249.550044] ffffffff9cbff170 ffff8801b3e6f358 ffffffff99489804 0000000000000000
> > [ 249.550044] ffff8801b3e50000 ffff8801b3e6f3b8 ffffffff9947dc97 0000000000000000
> > [ 249.550044] ffffffff00000001 ffff880100000001 ffffffff9cbff280 ffff8801b3e6f3b8
> > [ 249.550044] Call Trace:
> > [ 249.550044] dump_stack (lib/dump_stack.c:52)
> > [ 249.550044] print_usage_bug (kernel/locking/lockdep.c:2257)
> > [ 249.550044] ? print_irq_inversion_bug (kernel/locking/lockdep.c:2347)
> > [ 249.550044] mark_lock (kernel/locking/lockdep.c:2465 kernel/locking/lockdep.c:2920)
> > [ 249.550044] __lock_acquire (kernel/locking/lockdep.c:2821 kernel/locking/lockdep.c:3138)
> > [ 249.550044] ? preempt_count_sub (kernel/sched/core.c:2606)
> > [ 249.550044] ? blk_throtl_bio (include/linux/rcupdate.h:906 block/blk-throttle.c:1581)
> > [ 249.550044] ? blk_throtl_bio (include/linux/rcupdate.h:906 block/blk-throttle.c:1581)
> > [ 249.550044] ? rcu_lock_release (kernel/rcu/update.c:192)
> > [ 249.550044] ? blk_throtl_bio (include/linux/rcupdate.h:906 block/blk-throttle.c:1581)
> > [ 249.550044] lock_acquire (./arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3602)
> > [ 249.550044] ? zram_make_request (drivers/block/zram/zram_drv.c:1047)
> > [ 249.550044] down_read (./arch/x86/include/asm/rwsem.h:83 kernel/locking/rwsem.c:44)
> > [ 249.550044] ? zram_make_request (drivers/block/zram/zram_drv.c:1047)
> > [ 249.550044] ? _raw_spin_unlock (./arch/x86/include/asm/preempt.h:98 include/linux/spinlock_api_smp.h:152 kernel/locking/spinlock.c:183)
> > [ 249.550044] zram_make_request (drivers/block/zram/zram_drv.c:1047)
> > [ 249.550044] ? generic_make_request_checks (block/blk-core.c:1838)
> > [ 249.550044] ? put_lock_stats.isra.12 (./arch/x86/include/asm/preempt.h:98 kernel/locking/lockdep.c:254)
> > [ 249.550044] ? __test_set_page_writeback (include/linux/rcupdate.h:906 include/linux/memcontrol.h:171 mm/page-writeback.c:2418)
> > [ 249.550044] generic_make_request (block/blk-core.c:1917 (discriminator 1))
> > [ 249.550044] submit_bio (block/blk-core.c:1968)
> > [ 249.550044] ? __test_set_page_writeback (include/linux/rcupdate.h:906 include/linux/memcontrol.h:171 mm/page-writeback.c:2418)
> > [ 249.550044] __swap_writepage (mm/page_io.c:318)
> > [ 249.550044] ? page_swapcount (mm/swapfile.c:875)
> > [ 249.550044] ? get_parent_ip (kernel/sched/core.c:2550)
> > [ 249.550044] ? preempt_count_sub (kernel/sched/core.c:2606)
> > [ 249.550044] ? _raw_spin_unlock (./arch/x86/include/asm/preempt.h:98 include/linux/spinlock_api_smp.h:152 kernel/locking/spinlock.c:183)
> > [ 249.550044] ? page_swapcount (mm/swapfile.c:875)
> > [ 249.550044] swap_writepage (mm/page_io.c:249)
> > [ 249.550044] shmem_writepage (mm/shmem.c:823)
> > [ 249.550044] ? anon_vma_prepare (mm/rmap.c:448)
> > [ 249.550044] shrink_page_list (mm/vmscan.c:509 mm/vmscan.c:1021)
> > [ 249.550044] shrink_inactive_list (include/linux/spinlock.h:328 mm/vmscan.c:1526)
> > [ 249.550044] shrink_lruvec (mm/vmscan.c:1855 mm/vmscan.c:2103)
> > [ 249.550044] shrink_zone (mm/vmscan.c:2287)
> > [ 249.550044] kswapd_shrink_zone (include/linux/nodemask.h:131 include/linux/nodemask.h:131 mm/vmscan.c:2967)
> > [ 249.550044] balance_pgdat (mm/vmscan.c:3153)
> > [ 249.550044] kswapd (mm/vmscan.c:3359)
> > [ 249.550044] ? bit_waitqueue (kernel/sched/wait.c:291)
> > [ 249.550044] ? balance_pgdat (mm/vmscan.c:3276)
> > [ 249.550044] kthread (kernel/kthread.c:210)
> > [ 249.550044] ? put_lock_stats.isra.12 (./arch/x86/include/asm/preempt.h:98 kernel/locking/lockdep.c:254)
> > [ 249.550044] ? kthread_create_on_node (kernel/kthread.c:176)
> > [ 249.550044] ret_from_fork (arch/x86/kernel/entry_64.S:349)
> >
>
> Thanks for the report!
> I confirmed config didn't include lockdep at that time. :(
> /me slaps self.
>

My bad. I didn't test the original patch with lockdep enabled.

-ss

> This patch passed my test.
> Andrew, should I mark this patch as stable?
>
> --
> From e6ed83aa037a9828e8051c058bf29870be7b1431 Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@kernel.org>
> Date: Fri, 4 Jul 2014 08:58:05 +0900
> Subject: [PATCH] zram: avoid lockdep splat by revalidate_disk
>
> Sasha reported lockdep warning[1] introduced by [2].
>
> It could be fixed by doing disk revalidation out of the init_lock.
> It's okay because disk capacity change is protected by init_lock
> so that revalidate_disk always sees up-to-date value so there is
> no race.
>
> [1] https://lkml.org/lkml/2014/7/3/735
> [2] zram: revalidate disk after capacity change
>
> Reported-by: Sasha Levin <sasha.levin@oracle.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> drivers/block/zram/zram_drv.c | 22 ++++++++++++++++++----
> 1 file changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 6a4634b54207..dfa4024c448a 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -637,11 +637,18 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
> memset(&zram->stats, 0, sizeof(zram->stats));
>
> zram->disksize = 0;
> - if (reset_capacity) {
> + if (reset_capacity)
> set_capacity(zram->disk, 0);
> - revalidate_disk(zram->disk);
> - }
> +
> up_write(&zram->init_lock);
> +
> + /*
> + * Revalidate disk out of the init_lock to avoid lockdep splat.
> + * It's okay because disk's capacity is protected by init_lock
> + * so that revalidate_disk always sees up-to-date capacity.
> + */
> + if (reset_capacity)
> + revalidate_disk(zram->disk);
> }
>
> static ssize_t disksize_store(struct device *dev,
> @@ -681,8 +688,15 @@ static ssize_t disksize_store(struct device *dev,
> zram->comp = comp;
> zram->disksize = disksize;
> set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
> - revalidate_disk(zram->disk);
> up_write(&zram->init_lock);
> +
> + /*
> + * Revalidate disk out of the init_lock to avoid lockdep splat.
> + * It's okay because disk's capacity is protected by init_lock
> + * so that revalidate_disk always sees up-to-date capacity.
> + */
> + revalidate_disk(zram->disk);
> +
> return len;
>
> out_destroy_comp:
> --
> 2.0.0
>
> Kind regards,
> Minchan Kim
>


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