linux-kernel - [PATCH 5.15 109/913] Revert "mm: madvise: skip unmapped vma holes passed to process

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Date:   Tue,  5 Apr 2022 09:19:31 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Charan Teja Kalla <quic_charante@...cinc.com>,
        Michal Hocko <mhocko@...e.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Rientjes <rientjes@...gle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.15 109/913] Revert "mm: madvise: skip unmapped vma holes passed to process_madvise"

From: Charan Teja Kalla <quic_charante@...cinc.com>

commit e6b0a7b357659c332231621e4315658d062c23ee upstream.

This reverts commit 08095d6310a7 ("mm: madvise: skip unmapped vma holes
passed to process_madvise") as process_madvise() fails to return the
exact processed bytes in other cases too.

As an example: if process_madvise() hits mlocked pages after processing
some initial bytes passed in [start, end), it just returns EINVAL
although some bytes are processed.  Thus making an exception only for
ENOMEM is partially fixing the problem of returning the proper advised
bytes.

Thus revert this patch and return proper bytes advised.

Link: https://lkml.kernel.org/r/e73da1304a88b6a8a11907045117cccf4c2b8374.1648046642.git.quic_charante@quicinc.com
Fixes: 08095d6310a7ce ("mm: madvise: skip unmapped vma holes passed to process_madvise")
Signed-off-by: Charan Teja Kalla <quic_charante@...cinc.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Nadav Amit <nadav.amit@...il.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/madvise.c |    9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1287,16 +1287,9 @@ 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 && ret != -ENOMEM)
+		if (ret < 0)
 			break;
 		iov_iter_advance(&iter, iovec.iov_len);
 	}