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Date: Tue, 28 Jul 2015 08:32:26 -0700
From: Jaegeuk Kim <jaegeuk@kernel.org>
To: Chao Yu <chao2.yu@samsung.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: call set_page_dirty to attach i_wb
 for	cgroup
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On Tue, Jul 28, 2015 at 06:29:38PM +0800, Chao Yu wrote:
> Hi Jaegeuk,
> 
> > -----Original Message-----
> > From: Jaegeuk Kim [mailto:jaegeuk@kernel.org]
> > Sent: Sunday, July 26, 2015 8:21 AM
> > To: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org;
> > linux-f2fs-devel@lists.sourceforge.net
> > Cc: Jaegeuk Kim
> > Subject: [f2fs-dev] [PATCH 1/2] f2fs: call set_page_dirty to attach i_wb for cgroup
> > 
> > The cgroup attaches inode->i_wb via mark_inode_dirty and when set_page_writeback
> > is called, __inc_wb_stat() updates i_wb's stat.
> > 
> > So, we need to explicitly call set_page_dirty->__mark_inode_dirty in prior to
> > any writebacking pages.
> > 
> > This patch should resolve the following kernel panic reported by Andreas Reis.
> > 
> > https://bugzilla.kernel.org/show_bug.cgi?id=101801
> > 
> > --- Comment #2 from Andreas Reis <andreas.reis@gmail.com> ---
> > BUG: unable to handle kernel NULL pointer dereference at 00000000000000a8
> > IP: [<ffffffff8149deea>] __percpu_counter_add+0x1a/0x90
> > PGD 2951ff067 PUD 2df43f067 PMD 0
> > Oops: 0000 [#1] PREEMPT SMP
> > Modules linked in:
> > CPU: 7 PID: 10356 Comm: gcc Tainted: G        W       4.2.0-1-cu #1
> > Hardware name: Gigabyte Technology Co., Ltd. G1.Sniper M5/G1.Sniper M5, BIOS
> > T01 02/03/2015
> > task: ffff880295044f80 ti: ffff880295140000 task.ti: ffff880295140000
> > RIP: 0010:[<ffffffff8149deea>]  [<ffffffff8149deea>]
> > __percpu_counter_add+0x1a/0x90
> > RSP: 0018:ffff880295143ac8  EFLAGS: 00010082
> > RAX: 0000000000000003 RBX: ffffea000a526d40 RCX: 0000000000000001
> > RDX: 0000000000000020 RSI: 0000000000000001 RDI: 0000000000000088
> > RBP: ffff880295143ae8 R08: 0000000000000000 R09: ffff88008f69bb30
> > R10: 00000000fffffffa R11: 0000000000000000 R12: 0000000000000088
> > R13: 0000000000000001 R14: ffff88041d099000 R15: ffff880084a205d0
> > FS:  00007f8549374700(0000) GS:ffff88042f3c0000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00000000000000a8 CR3: 000000033e1d5000 CR4: 00000000001406e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Stack:
> >  0000000000000000 ffffea000a526d40 ffff880084a20738 ffff880084a20750
> >  ffff880295143b48 ffffffff811cc91e ffff880000000000 0000000000000296
> >  0000000000000000 ffff880417090198 0000000000000000 ffffea000a526d40
> > Call Trace:
> >  [<ffffffff811cc91e>] __test_set_page_writeback+0xde/0x1d0
> >  [<ffffffff813fee87>] do_write_data_page+0xe7/0x3a0
> >  [<ffffffff813faeea>] gc_data_segment+0x5aa/0x640
> >  [<ffffffff813fb0b8>] do_garbage_collect+0x138/0x150
> >  [<ffffffff813fb3fe>] f2fs_gc+0x1be/0x3e0
> >  [<ffffffff81405541>] f2fs_balance_fs+0x81/0x90
> >  [<ffffffff813ee357>] f2fs_unlink+0x47/0x1d0
> >  [<ffffffff81239329>] vfs_unlink+0x109/0x1b0
> >  [<ffffffff8123e3d7>] do_unlinkat+0x287/0x2c0
> >  [<ffffffff8123ebc6>] SyS_unlink+0x16/0x20
> >  [<ffffffff81942e2e>] entry_SYSCALL_64_fastpath+0x12/0x71
> > Code: 41 5e 5d c3 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 55 49
> > 89 f5 41 54 49 89 fc 53 48 83 ec 08 65 ff 05 e6 d9 b6 7e <48> 8b 47 20 48 63 ca
> > 65 8b 18 48 63 db 48 01 f3 48 39 cb 7d 0a
> > RIP  [<ffffffff8149deea>] __percpu_counter_add+0x1a/0x90
> >  RSP <ffff880295143ac8>
> > CR2: 00000000000000a8
> > ---[ end trace 5132449a58ed93a3 ]---
> > note: gcc[10356] exited with preempt_count 2
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> 
> Good catch!
> 
> Reviewed-by: Chao Yu <chao2.yu@samsung.com>

Oh, I've already requested for merge.

> 
> BTW, is this commit facd126d961d ("f2fs: fix wrong f2fs_put_page call for an error case")
> be submitted incorrectly? it seems not a good fix.

Oh, what is that? I was out of mind.
Thank you for pointing that out. :)

> 
> Thanks,
--
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