[PATCH] ext4 Fix setting random pages PageUptodate

[Markus Trippelsdorf <markus@trippelsdorf.de>]

On 2010.11.15 at 13:23 -0800, Hugh Dickins wrote:
> On Mon, Nov 15, 2010 at 11:54 AM, Markus Trippelsdorf
> <markus@trippelsdorf.de> wrote:
> > On 2010.11.15 at 13:38 +0100, Markus Trippelsdorf wrote:
> >> On 2010.11.12 at 13:20 +0100, Markus Trippelsdorf wrote:
> >> >
> >> > Yes. Fortunately the BUG is gone since I pulled the upcoming drm fixes
> >>
> >> No. I happend again today (with those fixes already applied):
> >>
> >> BUG: Bad page state in process knode  pfn:7f0a8
> >> page:ffffea0001bca4c0 count:0 mapcount:0 mapping:          (null) index:0x0
> >> page flags: 0x4000000000000008(uptodate)
> >> Pid: 18310, comm: knode Not tainted 2.6.37-rc1-00549-gae712bf-dirty #16
> >> Call Trace:
> >>  [<ffffffff810a9022>] ? bad_page+0x92/0xe0
> >>  [<ffffffff810aa240>] ? get_page_from_freelist+0x4b0/0x570
> >>  [<ffffffff8102e50e>] ? apic_timer_interrupt+0xe/0x20
> >>  [<ffffffff810aa413>] ? __alloc_pages_nodemask+0x113/0x6b0
> >>  [<ffffffff810a2dd4>] ? file_read_actor+0xc4/0x190
> >>  [<ffffffff810a4a70>] ? generic_file_aio_read+0x560/0x6b0
> >>  [<ffffffff810bdf8d>] ? handle_mm_fault+0x6bd/0x970
> >>  [<ffffffff8104b1d0>] ? do_page_fault+0x120/0x410
> >>  [<ffffffff810c3d85>] ? do_brk+0x275/0x360
> >>  [<ffffffff81452d8f>] ? page_fault+0x1f/0x30
> >> Disabling lock debugging due to kernel taint
> >
> > And another one. But this time it seems to point to ext4:
> >
> > BUG: Bad page state in process rm  pfn:52e54
> > page:ffffea0001222260 count:0 mapcount:0 mapping:          (null) index:0x0
> > page flags: 0x4000000000000008(uptodate)
> > Pid: 2084, comm: rm Not tainted 2.6.37-rc1-00549-gae712bf-dirty #23
> > Call Trace:
> >  [<ffffffff810a9022>] ? bad_page+0x92/0xe0
> >  [<ffffffff810aa240>] ? get_page_from_freelist+0x4b0/0x570
> >  [<ffffffff81142ae6>] ? ext4_ext_put_in_cache+0x46/0x90
> >  [<ffffffff810aa413>] ? __alloc_pages_nodemask+0x113/0x6b0
> >  [<ffffffff8118f0c7>] ? number.clone.2+0x2b7/0x2f0
> >  [<ffffffff810a38d5>] ? find_get_page+0x75/0xb0
> >  [<ffffffff810a4011>] ? find_or_create_page+0x51/0xb0
> >  [<ffffffff810ff4d7>] ? __getblk+0xd7/0x260
> >  [<ffffffff8113158f>] ? ext4_getblk+0x8f/0x1e0
> >  [<ffffffff811316ed>] ? ext4_bread+0xd/0x70
> >  [<ffffffff811369f4>] ? htree_dirblock_to_tree+0x34/0x190
> >  [<ffffffff8113870f>] ? ext4_htree_fill_tree+0x9f/0x250
> >  [<ffffffff810e109d>] ? do_filp_open+0x12d/0x5e0
> >  [<ffffffff811289ed>] ? ext4_readdir+0x14d/0x5a0
> >  [<ffffffff810e4e80>] ? filldir+0x0/0xd0
> >  [<ffffffff810e50a8>] ? vfs_readdir+0xa8/0xd0
> >  [<ffffffff810e4e80>] ? filldir+0x0/0xd0
> >  [<ffffffff810e51b1>] ? sys_getdents+0x81/0xf0
> >  [<ffffffff8102dc2b>] ? system_call_fastpath+0x16/0x1b
> > Disabling lock debugging due to kernel taint
> >
> > I don't know. Could a possible bug in linux/fs/ext4/page-io.c be
> > responsible for something like this?
> 
> I do think you're right: every one of your "Bad page state" reports
> has been complaining only about the PageUptodate bit being set, and
> that SetPageUpdate() in ext4_end_bio() does look suspicious, coming
> after the put_page().
> 
> The more suspicious given that other races have been noticed in
> precisely that area, and fixed with put_io_page() in the current git
> tree.
> 
> Perhaps that fixes your problem, but my guess would be not: I suspect
> the "if (!partial_write) SetPageUpdate(page);" should be done before
> the block (or put_io_page) which does the put_page().

ext4_end_bio calls put_page and kmem_cache_free before calling
SetPageUpdate(). This can result in setting the PageUptodate bit on
random pages and causes the following BUG:

 BUG: Bad page state in process rm  pfn:52e54
 page:ffffea0001222260 count:0 mapcount:0 mapping:          (null) index:0x0
 arch kernel: page flags: 0x4000000000000008(uptodate)

Fix the problem by moving put_io_page() after the SetPageUpdate() call.

Thanks to Hugh Dickins for analyzing this problem.

Reported-and-tested-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Markus Trippelsdorf <markus@trippelsdorf.de>

---
 fs/ext4/page-io.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 7f5451c..beacce1 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -237,8 +237,6 @@ static void ext4_end_bio(struct bio *bio, int error)
 			} while (bh != head);
 		}
 
-		put_io_page(io_end->pages[i]);
-
 		/*
 		 * If this is a partial write which happened to make
 		 * all buffers uptodate then we can optimize away a
@@ -248,6 +246,8 @@ static void ext4_end_bio(struct bio *bio, int error)
 		 */
 		if (!partial_write)
 			SetPageUptodate(page);
+
+		put_io_page(io_end->pages[i]);
 	}
 	io_end->num_io_pages = 0;
 	inode = io_end->inode;

-- 
Markus

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