Messages in this thread | | | Date | Mon, 22 Aug 2011 14:56:04 +0100 | From | Al Viro <> | Subject | Re: INFO: possible circular locking dependency detected 3.1.0-rc2-00190-g3210d19 |
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On Mon, Aug 22, 2011 at 09:33:34AM -0400, Josh Boyer wrote:
> So the lockdep report in the RHBZ (which now that I look at it > probably isn't the same as this report) seems to be doing a readdir > while find is trying to mmap, which is calling into > hugetlbfs_file_mmap and throwing the same deadlock warning. Is that > like the scenario you are describing above?
Lockdep records the first trace that leads to locks taken in this order. readdir() seems to be the first thing to step on i_mutex and mmap_sem (not too surprisingly, come to think of that - directory reads happening earlier in the boot than regular file writes).
So when it reports i_mutex taken under mmap_sem, readdir gets mentioned by lockdep. Often leading to comments along the lines of "but this inode is not a directory at all; shouldn't we relax the rules for non-directories?" Nope; the same ordering very much applies to regular files. With s/readdir/write/.
The bottom line is: don't take i_mutex while holding mmap_sem. Really.
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