Re: [PATCH] task_work: remove fifo ordering guarantee

From: yalin wang
Date: Mon Aug 31 2015 - 01:23:39 EST

> On Aug 30, 2015, at 01:08, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Sat, Aug 29, 2015 at 7:11 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
>> If this needs to be kept, maybe then add following, to make sure
>> we flush the list at most every BITS_PER_LONG files
> Hmm.
> I'm wondering if we should just make close_files() (or maybe even
> filp_close()) use a synchronous fput().
> Iirc, the reason we delay fput() is that we had some nasty issues for
> the generic fput case. It was called from interrupt context by the aio
> code, and just in general there's a lot of nasty cases that can cause
> the final fput to happen (so there are lockdep issues with the mmap
> locks because the last fput being from munmap etc).
> Maybe I forget some detail - it's been several years by now - but I
> think we could make the regular "close()" and "exit()" cases just use
> the synchronous fput (it's called "__fput_sync()" and currently
> explicitly limited to just kernel threads).
> Al?
> Because it feels all kinds of stupid to add things to the task-work
> queue just to then remove it almost immediately again. And
> close_files() is also called from various contexts. but the whole "put
> the final 'files_struct' case is certainly not at all as special as
> the 'put the final file'.
> Linus
> â
why not provide API like:
fput_nosync() ?

because synchronous version are reasonable and safe in most time,
let the user to select which version to use is more feasible, no matter if it is kthread or not.


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