Re: [patch] splice mmap_sem deadlock

[Jens Axboe <jens.axboe@oracle.com>]

On Fri, Sep 28 2007, Linus Torvalds wrote:
> 
> 
> On Fri, 28 Sep 2007, Linus Torvalds wrote:
> > 
> > So something like the appended might work. Untested.
> 
> Btw, it migth be cleaner to separate out this thing as a function of it's 
> own, ie something like
> 
>   /*
>    * Do a copy-from-user while holding the mmap_semaphore for reading
>    */
>   int copy_from_user_mmap_sem(void *dst, const void __user *src, size_t n)
>   {
> 	int partial;
> 
> 	pagefault_disable();
> 	partial = __copy_from_user_inatomic(dst, src, n);
> 	pagefault_enable();
> 
> 	if (!partial)
> 		return 0;
> 	up_read(&current->mm->mmap_sem);
> 	partial = copy_from_user(dst, src, n);
> 	down_read(&current->mm->mmap_sem);
> 
> 	return partial ? -EFAULT : 0;
>   }
> 
> in case anybody else needs it. And even if nobody else does, making it a 
> static inline function in fs/splice.c would at least separate out this 
> thing from the core functionality, and just help keep things clear.
> 
> Wanna test that thing?

Sure thing, I like this approach a lot more! I'll whip up a combo of
this and the previous and give it some testing. Don't expect a tested
patch before monday though, weekend fully booked...

-- 
Jens Axboe

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