linux-kernel - [PATCH 5.16 0113/1017] mm: madvise: skip unmapped vma holes passed to process

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Date:   Tue,  5 Apr 2022 09:17:06 +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>,
        David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Minchan Kim <minchan@...nel.org>,
        Nadav Amit <nadav.amit@...il.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.16 0113/1017] mm: madvise: skip unmapped vma holes passed to process_madvise

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

commit 08095d6310a7ce43256b4251577bc66a25c6e1a6 upstream.

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@...cinc.com>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Nadav Amit <nadav.amit@...il.com>
Cc: Stephen Rothwell <sfr@...b.auug.org.au>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
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, 8 insertions(+), 1 deletion(-)

--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1280,9 +1280,16 @@ 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);
 	}