Re: [patch 163/227] mm: madvise: skip unmapped vma holes passed to process_madvise

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On Tue, Mar 22, 2022 at 02:46:48PM -0700, Andrew Morton wrote:
> From: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
> Subject: mm: madvise: skip unmapped vma holes passed to process_madvise
> 
> The process_madvise() system call is expected to skip holes in vma passed
> through 'struct iovec' vector list.  But do_madvise, which
> process_madvise() calls for each vma, returns ENOMEM in case of unmapped
> holes, despite the VMA is processed.
> 
> Thus process_madvise() should treat ENOMEM as expected and consider the
> VMA passed to as processed and continue processing other vma's in the
> vector list.  Returning -ENOMEM to user, despite the VMA is processed,
> will be unable to figure out where to start the next madvise.
> 
> Link: https://lkml.kernel.org/r/4f091776142f2ebf7b94018146de72318474e686.1647008754.git.quic_charante@xxxxxxxxxxx

I thought it was still under discussion and Charan will post next
version along with previous patch
"mm: madvise: return correct bytes advised with process_madvise"

https://lore.kernel.org/linux-mm/7207b2f5-6b3e-aea4-aa1b-9c6d849abe34@xxxxxxxxxxx/


> Fixes: ecb8ac8b1f14("mm/madvise: introduce process_madvise() syscall: an external memory hinting API")
> Signed-off-by: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> 
>  mm/madvise.c |    9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> --- a/mm/madvise.c~mm-madvise-skip-unmapped-vma-holes-passed-to-process_madvise
> +++ a/mm/madvise.c
> @@ -1428,9 +1428,16 @@ SYSCALL_DEFINE5(process_madvise, int, pi
>  
>  	while (iov_iter_count(&iter)) {
>  		iovec = iov_iter_iovec(&iter);
> +		/*
> +		 * do_madvise returns ENOMEM if unmapped holes are present
> +		 * in the passed VMA. process_madvise() is expected to skip
> +		 * unmapped holes passed to it in the 'struct iovec' list
> +		 * and not fail because of them. Thus treat -ENOMEM return
> +		 * from do_madvise as valid and continue processing.
> +		 */
>  		ret = do_madvise(mm, (unsigned long)iovec.iov_base,
>  					iovec.iov_len, behavior);
> -		if (ret < 0)
> +		if (ret < 0 && ret != -ENOMEM)
>  			break;
>  		iov_iter_advance(&iter, iovec.iov_len);
>  	}
> _



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