linux-kernel - Re: zram: sleeping vunmap_pmd_range called from atomic zram_make

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Date:	Wed, 26 Mar 2014 14:21:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Minchan Kim <minchan@...nel.org>, ngupta@...are.org,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: zram: sleeping vunmap_pmd_range called from atomic
 zram_make_request

On Mon, 17 Mar 2014 15:56:09 -0400 Sasha Levin <sasha.levin@...cle.com> wrote:

> Hi all,
> 
> While fuzzing with trinity inside a KVM tools guest running the latest -next kernel
> I've stumbled on the following spew:
> 
> [  827.272181] BUG: sleeping function called from invalid context at mm/vmalloc.c:74
> [  827.273204] in_atomic(): 1, irqs_disabled(): 0, pid: 4213, name: kswapd14
> [  827.274080] 1 lock held by kswapd14/4213:
> [  827.274587]  #0:  (&zram->init_lock){++++.-}, at: zram_make_request (drivers/block/zram/zram_drv.c:765)
> [  827.275923] Preemption disabled zram_bvec_write (drivers/block/zram/zram_drv.c:500)
> [  827.276910]
> [  827.277104] CPU: 30 PID: 4213 Comm: kswapd14 Tainted: G        W     3.14.0-rc6-next-20140317-sasha-00012-ge933921-dirty #226
> [  827.278467]  ffff880229700000 ffff8802296fd388 ffffffff8449ebb3 0000000000000001
> [  827.279610]  0000000000000000 ffff8802296fd3b8 ffffffff81176cec ffff8802296fd3c8
> [  827.281258]
> [  827.281549]  ffff88032b40a000 ffffc900077fa000 ffffc900077f8000 ffff8802296fd428
> [  827.282911] Call Trace:
> [  827.283318]  dump_stack (lib/dump_stack.c:52)
> [  827.284013]  __might_sleep (kernel/sched/core.c:7016)
> [  827.284797]  vunmap_pmd_range (mm/vmalloc.c:74)

I expect this was caused by
mm-vmalloc-avoid-soft-lockup-warnings-when-vunmaping-large-ranges.patch
and its folloup
mm-vmalloc-avoid-soft-lockup-warnings-when-vunmaping-large-ranges-fix.patch.

The second patch proved that the first patch can't add cond_resched()
in the vunmap_page_range() path.  I dropped both patches on March 18th.


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