Suparna Bhattacharya wrote:
A new DIO flag is added into our distribution (2.6.9 based) to work
around the problem by moving the inode semaphore acquiring within
__blockdev_direct_IO() (patch attached) into GFS code path (so lock
order can be re-arranged). The new lock granularity is not ideal but it
gets us out of this deadlock.
Could you help me understand in a little more detail why DIO_OWN_LOCKING
does not work for you ? Is the releasing of i_sem during READ a problem ?
Doesn't holding i_sem for the entire duration of IO for read slow down
concurrent DIO reads to different parts of the file ?
We don't mess around with i_sem during read. So that piece of locking
code is ok (but I have to say it looks very messy). The thing we can't
work around is #518 in get_more_blocks() (from 2.6.9 base code so line
offset may be different but you can get the idea):
491 static int get_more_blocks(struct dio *dio)
492 {
493 int ret;
......
516
517 create = dio->rw == WRITE;
518 if ((dio->lock_type == DIO_LOCKING) ||
(dio->lock_type = = DIO_CLUSTER_LOCKING)) {
519 if (dio->block_in_file <
(i_size_read(dio->inode ) >>
520
dio->blkbits))
521 create = 0;
522 } else if (dio->lock_type == DIO_NO_LOCKING) {
523 create = 0;
524 }
One of the things I wanted to achieve in the proposal was to avoid
the need for these various locking mode flag checks in the DIO code,
leaving it to the higher level to just select the right entry points,
i.e. the _nolock or lock versions of generic_file_aio_write et al.
That's a good news - these DIO locking flags are all last-minute
bandaids anyway.
Would appreciate your thoughts on this, once you've had a chance to
go throught it.
On the road all next week but will get to it when I'm back to office. On
the other hand, thank you for looking into this.
-- Wendy
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