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Date: Fri, 20 Apr 2012 19:49:44 +0200
From: Jens Axboe <axboe@kernel.dk>
MIME-Version: 1.0
Subject: Re: fio causing kernel panic due to zero size requests
References: <CAKa9NmuEcJu7U+M8s4O2C0QPHzpMQE9a0zctfcahP=Q-qq9UCA@mail.gmail.com>
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To: Vikram Seth <seth.vik@gmail.com>
Cc: fio@vger.kernel.org

On 2012-04-20 19:27, Vikram Seth wrote:
> Hi Jens,
> 
> Recently we saw an issue where fio created kernel panic because of 0
> size requests.
> Pasting the stack trace below.
> 
> <d>Pid: 13846, comm: fio Tainted: P M 2.6.38.4-
> <d>RIP: 0010:[<ffffffff8111d90d>] [<ffffffff8111d90d>]
> __blockdev_direct_IO+0x6a7/0x9ce
> <d>RSP: 0018:ffff8823fb7e9c18 EFLAGS: 00010246
> <d>RAX: 0000000000000000 RBX: ffffea007d55d460 RCX: 000000000000000a
> <d>RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffff8812342b80e0
> <d>RBP: ffff8823fb7e9cd8 R08: 0000000000000001 R09: 0000000000000000
> <d>R10: 0000000000000000 R11: ffffea0000000000 R12: ffff881233d64400
> <d>R13: 0000000000000003 R14: ffff881233d64498 R15: ffff8812342b80e0
> <d>FS: 00007f048cddb6e0(0000) GS:ffff88007e200000(0000) knlGS:0000000000000000
> <d>CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> <d>CR2: 000000000040d040 CR3: 000000238ea69000 CR4: 00000000000406f0
> <d>DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> <d>DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process fio (pid: 13846, threadinfo ffff8823fb7e8000, task ffff882432ead120)
> <0>Stack:
> <c> ffff8823fb7e9c68<c> ffffffff814478ce<c> ffff882300000001<c>
> ffff8823cf614000<c>
> <c> ffff882300000004<c> ffffffff814478ce<c> fffffffffffffc00<c>
> 00000000814478ce<c>
> <c> ffff8823fb7e8000<c> 0000000000000400<c> 0000000a00000001<c>
> ffff8823fb7e8000<c>
> 
> Checking that function it's
> 
> 0xffffffff8111d90d is in __blockdev_direct_IO (fs/direct-io.c:955).
> 
> and that points to following line in direct-io.c:
> 
>  955             BUG_ON(this_chunk_bytes == 0);
> 
> We also tested with following patch from kernel.org
> 
> f9b5570 fs: simplify handling of zero sized reads in __blockdev_direct_IO
> 
> That resolved the panic problem.
> 
> Can you please add check to fio that it should error out OR skip 0
> size accesses ?

It seems you forgot to include the job file that triggered this :-)
Fio should not be making zero sized reads, but pretty embarassing that
the kernel oopsed on getting one. It could be a file system issue, a bug
there triggering a zero sized read.

So how did you trigger this? And on what fs?

-- 
Jens Axboe