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    SubjectRe: 3.11.4: kernel BUG at fs/buffer.c:1268
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    On Oct 17, 2013, at 4:14 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
    > On Thu, Oct 17, 2013 at 05:11:43PM -0400, George Spelvin wrote:
    >>
    >> Well, it happened again (error appended). Can you please clarify what you mean
    >> by "such BUG_ON()"; I'm having a hard time following the RCU code and determining
    >> all the situations under which __fput() might be called.
    >
    > __fput() can be called via task_work_run() or via schedule_work(). That's
    > all. And it certainly should never be called with interrupts disabled.
    > So stick BUG_ON(irqs_disabled()) in it (WARN_ON() might be better, but
    > not by much).
    >
    > There are two ways these traces could've happened:
    > * exit_task_work() called by do_exit() with irqs disabled.
    > Definitely buggy (and would do really nasty things to several functions
    > called by do_exit() before that one).
    > * __fput() is called with irqs enabled, but somewhere on the
    > way into ext4 (dput -> iput -> evict inode -> free blocks, now that
    > unlinked file got closed -> ...) we manage to disable irqs and forget
    > to enable them.

    IMHO the most common case of "BUG: sleeping function called from
    invalid context” is due to stack overflow. This corrupts the task
    struct, and incorrectly sets the “in_interrupt” bit.

    What kind of storage stack is underneath this filesystem? If
    it is deep (e.g. DM + LVM + iSCSI) then the stack overflow is
    definitely possible.

    There were also a discussion by Christoph of page allocation
    recursing into the fs again (in "xfs: prevent stack overflows
    from page cache allocation”) though I’m not sure if that applies
    to ext4 or not.

    Cheers, Andreas





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