linux-kernel - Re: [PATCH] block devices: validate block device capacity

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Date:	Thu, 30 Jan 2014 14:49:23 -0800
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>,
	"Alasdair G. Kergon" <agk@...hat.com>,
	Mike Snitzer <msnitzer@...hat.com>, dm-devel@...hat.com,
	Nick Piggin <npiggin@...nel.dk>,
	"David S. Miller" <davem@...emloft.net>, linux-ide@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Neil Brown <neilb@...e.de>, linux-raid@...r.kernel.org
Subject: Re: [PATCH] block devices: validate block device capacity

On Thu, 2014-01-30 at 15:40 -0500, Mikulas Patocka wrote:
> When running the LVM2 testsuite on 32-bit kernel, there are unkillable
> processes stuck in the kernel consuming 100% CPU:
> blkid           R running      0  2005   1409 0x00000004
> ce009d00 00000082 ffffffcf c11280ba 00000060 560b5dfd 00003111 00fe41cb
> 00000000 ce009d00 00000000 d51cfeb0 00000000 0000001e 00000002 ffffffff
> 00000002 c10748c1 00000002 c106cca4 00000000 00000000 ffffffff 00000000
> Call Trace:
> [<c11280ba>] ? radix_tree_next_chunk+0xda/0x2c0
> [<c10748c1>] ? release_pages+0x61/0x160
> [<c106cca4>] ? find_get_pages+0x84/0x100
> [<c1251fbe>] ? _cond_resched+0x1e/0x40
> [<c10758cb>] ? truncate_inode_pages_range+0x12b/0x440
> [<c1075cb7>] ? truncate_inode_pages+0x17/0x20
> [<c10cf2ba>] ? __blkdev_put+0x3a/0x140
> [<c10d02db>] ? blkdev_close+0x1b/0x40
> [<c10a60b2>] ? __fput+0x72/0x1c0
> [<c1039461>] ? task_work_run+0x61/0xa0
> [<c1253b6f>] ? work_notifysig+0x24/0x35
> 
> This is caused by the fact that the LVM2 testsuite creates 64TB device.
> The kernel uses "unsigned long" to index pages in files and block devices,
> on 64TB device "unsigned long" overflows (it can address up to 16TB with
> 4k pages), causing the infinite loop.

Why is this?  the whole reason for CONFIG_LBDAF is supposed to be to
allow 64 bit offsets for block devices on 32 bit.  It sounds like
there's somewhere not using sector_t ... or using it wrongly which needs
fixing.

> On 32-bit architectures, we must limit block device size to
> PAGE_SIZE*(2^32-1).

So you're saying CONFIG_LBDAF can never work, why?

James



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