Messages in this thread | | | Date | Sat, 26 Apr 2008 03:41:39 -0700 | From | Andrew Morton <> | Subject | Re: Possible race between direct IO and JBD? |
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On Fri, 25 Apr 2008 16:38:23 -0700 Mingming Cao <cmm@us.ibm.com> wrote:
> Hi, > > While looking at a bug related to direct IO returns to EIO, after > looking at the code, I found there is a window that > try_to_free_buffers() from direct IO could race with JBD, which holds > the reference to the data buffers before journal_commit_transaction() > ensures the data buffers has reached to the disk. > > A little more detail: to prepare for direct IO, generic_file_direct_IO() > calls invalidate_inode_pages2_range() to invalidate the pages in the > cache before performaning direct IO. invalidate_inode_pages2_range() > tries to free the buffers via try_to free_buffers(), but sometimes it > can't, due to the buffers is possible still on some transaction's > t_sync_datalist or t_locked_list waiting for > journal_commit_transaction() to process it. > > Currently Direct IO simply returns EIO if try_to_free_buffers() finds > the buffer is busy, as it has no clue that JBD is referencing it. > > Is this a known issue and expected behavior? Any thoughts?
Something like that might be possible, although people used to test buffered-vs-direct fairly heavily.
generic_file_direct_IO() will run filemap_write_and_wait()->filemap_fdatawrite() under i_mutex, and this should run commits, write back dirty pages, etc.
There might remain races though, perhaps with page faults.
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