Re: Lockdep complain for zram

From: Nitin Gupta
Date: Wed Nov 21 2012 - 13:06:26 EST

On 11/21/2012 12:37 AM, Minchan Kim wrote:
Hi alls,

Today, I saw below complain of lockdep.
As a matter of fact, I knew it long time ago but forgot that.
The reason lockdep complains is that now zram uses GFP_KERNEL
in reclaim path(ex, __zram_make_request) :(
I can fix it via replacing GFP_KERNEL with GFP_NOIO.
But more big problem is vzalloc in zram_init_device which calls GFP_KERNEL.
Of course, I can change it with __vmalloc which can receive gfp_t.
But still we have a problem. Althoug __vmalloc can handle gfp_t, it calls
allocation of GFP_KERNEL. That's why I sent the patch.
https://lkml.org/lkml/2012/4/23/77
Since then, I forgot it, saw the bug today and poped the question again.

Yes. Fundamental problem is utter crap API vmalloc.
If we can fix it, everyone would be happy. But life isn't simple like seeing
my thread of the patch.

So next option is to move zram_init_device into setting disksize time.
But it makes unnecessary metadata waste until zram is used really(That's why
Nitin move zram_init_device from disksize setting time to make_request) and
it makes user should set the disksize before using, which are behavior change.

I would like to clean up this issue before promoting because it might change
usage behavior.

Do you have any idea?


Maybe we can alloc_vm_area() right on device creation in create_device() assuming the default disksize. If user explicitly sets the disksize, this vm area is deallocated and a new one is allocated based on the new disksize. When the device is reset, we should only free physical pages allocated for the table and the virtual area should be set back as if disksize is set to the default.

At the device init time, all the pages can be allocated with GFP_NOIO | __GPF_HIGHMEM and since the VM area is preallocated, map_vm_area() will not hit any of those page-table allocations with GFP_KERNEL.

Other allocations made directly from zram, for instance in the partial I/O case, should also be changed to GFP_NOIO | __GFP_HIGHMEM.

Thanks,
Nitin

============ 8< ==============


[ 335.772277] =================================
[ 335.772615] [ INFO: inconsistent lock state ]
[ 335.772955] 3.7.0-rc6 #162 Tainted: G C
[ 335.773320] ---------------------------------
[ 335.773663] inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-R} usage.
[ 335.774170] kswapd0/23 [HC0[0]:SC0[0]:HE1:SE1] takes:
[ 335.774564] (&zram->init_lock){+++++-}, at: [<ffffffffa0009d0a>] zram_make_request+0x4a/0x260 [zram]
[ 335.775321] {RECLAIM_FS-ON-W} state was registered at:
[ 335.775716] [<ffffffff81099532>] mark_held_locks+0x82/0x130
[ 335.776009] [<ffffffff81099c47>] lockdep_trace_alloc+0x67/0xc0
[ 335.776009] [<ffffffff811189d4>] __alloc_pages_nodemask+0x94/0xa00
[ 335.776009] [<ffffffff81152806>] alloc_pages_current+0xb6/0x120
[ 335.776009] [<ffffffff811143d4>] __get_free_pages+0x14/0x50
[ 335.776009] [<ffffffff81157dff>] kmalloc_order_trace+0x3f/0xf0
[ 335.776009] [<ffffffffa0009b1b>] zram_init_device+0x7b/0x220 [zram]
[ 335.776009] [<ffffffffa0009f0a>] zram_make_request+0x24a/0x260 [zram]
[ 335.776009] [<ffffffff81299d8a>] generic_make_request+0xca/0x100
[ 335.776009] [<ffffffff81299e3b>] submit_bio+0x7b/0x160
[ 335.776009] [<ffffffff81197b92>] submit_bh+0xf2/0x120
[ 335.776009] [<ffffffff8119b855>] block_read_full_page+0x235/0x3a0
[ 335.776009] [<ffffffff8119efc8>] blkdev_readpage+0x18/0x20
[ 335.776009] [<ffffffff8111c107>] __do_page_cache_readahead+0x2c7/0x2d0
[ 335.776009] [<ffffffff8111c249>] force_page_cache_readahead+0x79/0xb0
[ 335.776009] [<ffffffff8111c683>] page_cache_sync_readahead+0x43/0x50
[ 335.776009] [<ffffffff81111490>] generic_file_aio_read+0x4f0/0x760
[ 335.776009] [<ffffffff8119ffbb>] blkdev_aio_read+0xbb/0xf0
[ 335.776009] [<ffffffff811661f3>] do_sync_read+0xa3/0xe0
[ 335.776009] [<ffffffff81166910>] vfs_read+0xb0/0x180
[ 335.776009] [<ffffffff81166a32>] sys_read+0x52/0xa0
[ 335.776009] [<ffffffff8155a982>] system_call_fastpath+0x16/0x1b
[ 335.776009] irq event stamp: 97589
[ 335.776009] hardirqs last enabled at (97589): [<ffffffff812b3374>] throtl_update_dispatch_stats+0x94/0xf0
[ 335.776009] hardirqs last disabled at (97588): [<ffffffff812b332d>] throtl_update_dispatch_stats+0x4d/0xf0
[ 335.776009] softirqs last enabled at (67416): [<ffffffff81046c59>] __do_softirq+0x139/0x280
[ 335.776009] softirqs last disabled at (67395): [<ffffffff8155bb0c>] call_softirq+0x1c/0x30
[ 335.776009]
[ 335.776009] other info that might help us debug this:
[ 335.776009] Possible unsafe locking scenario:
[ 335.776009]
[ 335.776009] CPU0
[ 335.776009] ----
[ 335.776009] lock(&zram->init_lock);
[ 335.776009] <Interrupt>
[ 335.776009] lock(&zram->init_lock);
[ 335.776009]
[ 335.776009] *** DEADLOCK ***
[ 335.776009]
[ 335.776009] no locks held by kswapd0/23.
[ 335.776009]
[ 335.776009] stack backtrace:
[ 335.776009] Pid: 23, comm: kswapd0 Tainted: G C 3.7.0-rc6 #162
[ 335.776009] Call Trace:
[ 335.776009] [<ffffffff81547ff7>] print_usage_bug+0x1f5/0x206
[ 335.776009] [<ffffffff8100f90f>] ? save_stack_trace+0x2f/0x50
[ 335.776009] [<ffffffff81096a65>] mark_lock+0x295/0x2f0
[ 335.776009] [<ffffffff81095e90>] ? print_irq_inversion_bug.part.37+0x1f0/0x1f0
[ 335.776009] [<ffffffff812b4af8>] ? blk_throtl_bio+0x88/0x630
[ 335.776009] [<ffffffff81097024>] __lock_acquire+0x564/0x1c00
[ 335.776009] [<ffffffff810996e5>] ? trace_hardirqs_on_caller+0x105/0x190
[ 335.776009] [<ffffffff812b4e32>] ? blk_throtl_bio+0x3c2/0x630
[ 335.776009] [<ffffffff812b4af8>] ? blk_throtl_bio+0x88/0x630
[ 335.776009] [<ffffffff812a101c>] ? create_task_io_context+0xdc/0x150
[ 335.776009] [<ffffffff812a101c>] ? create_task_io_context+0xdc/0x150
[ 335.776009] [<ffffffffa0009d0a>] ? zram_make_request+0x4a/0x260 [zram]
[ 335.776009] [<ffffffff81098c85>] lock_acquire+0x85/0x130
[ 335.776009] [<ffffffffa0009d0a>] ? zram_make_request+0x4a/0x260 [zram]
[ 335.776009] [<ffffffff8154f87c>] down_read+0x4c/0x61
[ 335.776009] [<ffffffffa0009d0a>] ? zram_make_request+0x4a/0x260 [zram]
[ 335.776009] [<ffffffff81299ac2>] ? generic_make_request_checks+0x222/0x420
[ 335.776009] [<ffffffff8111a4fe>] ? test_set_page_writeback+0x6e/0x1a0
[ 335.776009] [<ffffffffa0009d0a>] zram_make_request+0x4a/0x260 [zram]
[ 335.776009] [<ffffffff81299d8a>] generic_make_request+0xca/0x100
[ 335.776009] [<ffffffff81299e3b>] submit_bio+0x7b/0x160
[ 335.776009] [<ffffffff81119423>] ? account_page_writeback+0x13/0x20
[ 335.776009] [<ffffffff8111a585>] ? test_set_page_writeback+0xf5/0x1a0
[ 335.776009] [<ffffffff81148aa9>] swap_writepage+0x1b9/0x240
[ 335.776009] [<ffffffff81149bf5>] ? __swap_duplicate+0x65/0x170
[ 335.776009] [<ffffffff8112715a>] ? shmem_writepage+0x17a/0x2f0
[ 335.776009] [<ffffffff8112715a>] ? shmem_writepage+0x17a/0x2f0
[ 335.776009] [<ffffffff8154f411>] ? __mutex_unlock_slowpath+0xd1/0x160
[ 335.776009] [<ffffffff810996e5>] ? trace_hardirqs_on_caller+0x105/0x190
[ 335.776009] [<ffffffff8109977d>] ? trace_hardirqs_on+0xd/0x10
[ 335.776009] [<ffffffff81127195>] shmem_writepage+0x1b5/0x2f0
[ 335.776009] [<ffffffff81122b96>] shrink_page_list+0x516/0x9a0
[ 335.776009] [<ffffffff8111ca20>] ? __activate_page+0x150/0x150
[ 335.776009] [<ffffffff811235c7>] shrink_inactive_list+0x1f7/0x3f0
[ 335.776009] [<ffffffff81123f05>] shrink_lruvec+0x435/0x540
[ 335.776009] [<ffffffff81065050>] ? __init_waitqueue_head+0x60/0x60
[ 335.776009] [<ffffffff81125093>] kswapd+0x703/0xc80
[ 335.776009] [<ffffffff81551dd0>] ? _raw_spin_unlock_irq+0x30/0x50
[ 335.776009] [<ffffffff81065050>] ? __init_waitqueue_head+0x60/0x60
[ 335.776009] [<ffffffff81124990>] ? try_to_free_pages+0x6f0/0x6f0
[ 335.776009] [<ffffffff810646ea>] kthread+0xea/0xf0
[ 335.776009] [<ffffffff81064600>] ? flush_kthread_work+0x1a0/0x1a0
[ 335.776009] [<ffffffff8155a8dc>] ret_from_fork+0x7c/0xb0
[ 335.776009] [<ffffffff81064600>] ? flush_kthread_work+0x1a0/0x1a0



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