linux-kernel - [RFC PATCH 3/8] mm/madvise: remove unnecessary checks on madvise_free_single

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Date:   Sun, 26 Sep 2021 09:12:54 -0700
From:   Nadav Amit <nadav.amit@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Peter Xu <peterx@...hat.com>, Nadav Amit <namit@...are.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Minchan Kim <minchan@...nel.org>,
        Colin Cross <ccross@...gle.com>,
        Suren Baghdasarya <surenb@...gle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>
Subject: [RFC PATCH 3/8] mm/madvise: remove unnecessary checks on madvise_free_single_vma()

From: Nadav Amit <namit@...are.com>

madvise_free_single_vma() currently rechecks that the range fits within
the VMA, adapts it accordingly, and returns -EINVAL if the range is
entirely outside of the VMA.

The error-code of -EINVAL is incorrect according to the man pages (as it
should have been -ENOMEM), but anyhow the range that is provided to
madvise_free_single_vma() should always be valid. It is set correctly in
do_madvise() and then rechecked in madvise_dontneed_free() is the
mmap-lock is dropped.

Remove this check.

Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Colin Cross <ccross@...gle.com>
Cc: Suren Baghdasarya <surenb@...gle.com>
Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
Signed-off-by: Nadav Amit <namit@...are.com>
---
 mm/madvise.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index fe843513a4e8..17e39c70704b 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -716,14 +716,8 @@ static int madvise_free_single_vma(struct vm_area_struct *vma,
 	if (!vma_is_anonymous(vma))
 		return -EINVAL;
 
-	range.start = max(vma->vm_start, start_addr);
-	if (range.start >= vma->vm_end)
-		return -EINVAL;
-	range.end = min(vma->vm_end, end_addr);
-	if (range.end <= vma->vm_start)
-		return -EINVAL;
 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,
-				range.start, range.end);
+				start_addr, end_addr);
 
 	lru_add_drain();
 	tlb_gather_mmu(&tlb, mm);
-- 
2.25.1