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Date: Mon, 22 Aug 2011 10:30:02 -0700 From: Aditya Kali <adityakali@...gle.com> To: Yongqiang Yang <xiaoqiangnk@...il.com> Cc: Jan Kara <jack@...e.cz>, "Ted Ts'o" <tytso@....edu>, Ext4 Developers List <linux-ext4@...r.kernel.org> Subject: Re: attempt to fix race in bigalloc code path On Mon, Aug 22, 2011 at 6:54 AM, Yongqiang Yang <xiaoqiangnk@...il.com> wrote: > Hi, > > I can not find the patch - attempt to fix race in bigalloc code path - > in the mailing list. > > I don't think this patch can work. set_buffers_da_mapped() is called > under i_data_sem, so it can not lock page. If the page is not locked, > calling page_has_buffers() is not secure as Jan pointed out > previously. If a page is partially mapped(block size < page size), > setting BH_Da_Mapped without locking page is not safe too. > The BH_Da_Mapped is set only during page writeback when the page is locked (in write_cache_pages_da). So, the setting of BH_Da_Mapped should be safe, no ? > BTW: find_delalloc_range() does not lock page as ext4_fiemap_cb(). > As Jan said, it can crash system. BUT we can not lock page in both > scenarios, because i_data_sem is hold. So delayed extent list is > necessary. I have finished the code implementing delayed extent list, > which needs some further testing. > > > What are your opinions? > I agree that having a delayed extent list will greatly simply this solution in this case. > > -- > Best Wishes > Yongqiang Yang > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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