Re: [PATCH v3 1/3] iomap: resched ioend completion when in non-atomic context

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On Mon, May 24, 2021 at 07:57:48AM -0400, Brian Foster wrote:
> On Sat, May 22, 2021 at 03:45:11PM +0800, Ming Lei wrote:
> > On Mon, May 17, 2021 at 01:17:20PM -0400, Brian Foster wrote:
> > > The iomap ioend mechanism has the ability to construct very large,
> > > contiguous bios and/or bio chains. This has been reported to lead to
> > 
> > BTW, it is actually wrong to complete a large bio chains in
> > iomap_finish_ioend(), which may risk in bio allocation deadlock, cause
> > bio_alloc_bioset() relies on bio submission to make forward progress. But
> > it becomes not true when all chained bios are freed just after the whole
> > ioend is done since all chained bios(except for the one embedded in ioend)
> > are allocated from same bioset(fs_bio_set).
> > 
> 
> Interesting. Do you have a reproducer (or error report) for this? Is it

No, but the theory has been applied for long time.

> addressed by the next patch, or are further changes required?

Your patchset can't address the issue.


Thanks,
Ming




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