+ mm-madvise-skip-unmapped-vma-holes-passed-to-process_madvise.patch added to -mm tree

+ mm-madvise-skip-unmapped-vma-holes-passed-to-process_madvise.patch added to -mm tree

[Andrew Morton]

The patch titled
     Subject: mm: madvise: skip unmapped vma holes passed to process_madvise
has been added to the -mm tree.  Its filename is
     mm-madvise-skip-unmapped-vma-holes-passed-to-process_madvise.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-madvise-skip-unmapped-vma-holes-passed-to-process_madvise.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-madvise-skip-unmapped-vma-holes-passed-to-process_madvise.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Charan Teja Kalla <quic_charante@quicinc.com>
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@quicinc.com
Fixes: ecb8ac8b1f14("mm/madvise: introduce process_madvise() syscall: an external memory hinting API")
Signed-off-by: Charan Teja Kalla <quic_charante@quicinc.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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);
 	}
_

Patches currently in -mm which might be from quic_charante@quicinc.com are

mm-vmscan-fix-documentation-for-page_check_references.patch
mm-madvise-return-correct-bytes-advised-with-process_madvise.patch
mm-madvise-skip-unmapped-vma-holes-passed-to-process_madvise.patch