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    DateThu, 22 Mar 2007 15:18:13 +1100
    FromNick Piggin <>
    SubjectRe: [1/6] 2.6.21-rc4: known regressions
    Linus Torvalds wrote:
    
    > In contrast, the hang reported by Mariusz Kozlowski has a slightly 
    > different feel to it, but there's a tantalizing pattern in there too:
    > 
    >   http://www.ussg.iu.edu/hypermail/linux/kernel/0703.0/1243.html
    > 
    > 	Call Trace:
    > 	[<c03ec87e>] io_schedule+0x42/0x59
    > 	[<c0184915>] sleep_on_buffer+0x8/0xc
    > 	[<c03ed217>] __wait_on_bit+0x47/0x6c
    > 	[<c03ed297>] out_of_line_wait_on_bit+0x5b/0x64
    > 	[<c01848a8>] __wait_on_buffer+0x27/0x2d
    > 	[<c01b4228>] journal_commit_transaction+0x707/0x127f
    > 	[<c01b868b>] kjournald+0xac/0x1ed
    > 	[<c0126af5>] kthread+0xa2/0xc9
    > 	[<c010422b>] kernel_thread_helper+0x7/0x1c
    > 
    > which certainly also looks like an IO never completed (or completed but 
    > never woke anything up).
    > 
    > It also seems to be related to *buffers*. Maybe the whole bh layer thing 
    > is a fluke, but it's not waiting for normal data, it's very much waiting 
    > for those journal things that all use buffer heads.Which just makes me 
    > worry about those patches by Nick (which did come in through Andrew). I 
    > don't think it's the memorder one (it looks safe and shouldn't matter on 
    > x86 anyway!), but what about the
    > 
    > 	fs: fix __block_write_full_page error case buffer submission
    > 
    > locking change for example? Or that "fs: fix nobh data leak" thing with 
    > its fix? It uses "SetPageUptodate(page);" without waking up anybody who 
    > might wait for it (but the waiters here seem to wait on buffers, so that's 
    > probably not it)..
    
    Nothing sleeps on PageUptodate, so I don't think that could explain it.
    
    The fs: fix __block_write_full_page error case buffer submission patch
    does change the locking, but I'd be really suprised if that was the
    problem, because it changes locking to match the regular non-error path
    submission.
    
    It could be possible that ext3 is doing something weird and expecting
    the old behaviour if it failed get_block, but that seems pretty weird
    to do, and would need fixing.
    
    fs: nobh data leak... again hard to see how it could cause an unlock/wakeup
    to get lost. Is Mariusz using the nobh mount option?
    
    It wouldn't hurt to test with these patches backed out...
    
    > Alternatively, maybe it really is an _io_ problem (and the buffer-head 
    > thing is just a red herring, and it could happen to other IO, it's just 
    > that metadata IO uses buffer heads), and it's the scheduler changes since 
    > 2.6.20..
    
    I see what you mean. Could it be an ext3 or jbd change I wonder?
    
    -- 
    SUSE Labs, Novell Inc.
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