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From: Jann Horn <jannh@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Oleg Nesterov <oleg@redhat.com>
Subject: [PATCH v4 5/5] mm/gup: Take mmap_lock in get_dump_page()
Date: Wed, 26 Aug 2020 17:14:48 +0200	[thread overview]
Message-ID: <20200826151448.3404695-6-jannh@google.com> (raw)
In-Reply-To: <20200826151448.3404695-1-jannh@google.com>

Properly take the mmap_lock before calling into the GUP code from
get_dump_page(); and play nice, allowing the GUP code to drop the mmap_lock
if it has to sleep.

As Linus pointed out, we don't actually need the VMA because
__get_user_pages() will flush the dcache for us if necessary.

Signed-off-by: Jann Horn <jannh@google.com>
---
 mm/gup.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 92519e5a44b3..bd0f7311c5c6 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1552,19 +1552,23 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
  * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
  * allowing a hole to be left in the corefile to save diskspace.
  *
- * Called without mmap_lock, but after all other threads have been killed.
+ * Called without mmap_lock (takes and releases the mmap_lock by itself).
  */
 #ifdef CONFIG_ELF_CORE
 struct page *get_dump_page(unsigned long addr)
 {
-	struct vm_area_struct *vma;
+	struct mm_struct *mm = current->mm;
 	struct page *page;
+	int locked = 1;
+	int ret;
 
-	if (__get_user_pages_locked(current->mm, addr, 1, &page, &vma, NULL,
-				    FOLL_FORCE | FOLL_DUMP | FOLL_GET) < 1)
+	if (mmap_read_lock_killable(mm))
 		return NULL;
-	flush_cache_page(vma, addr, page_to_pfn(page));
-	return page;
+	ret = __get_user_pages_locked(mm, addr, 1, &page, NULL, &locked,
+				      FOLL_FORCE | FOLL_DUMP | FOLL_GET);
+	if (locked)
+		mmap_read_unlock(mm);
+	return (ret == 1) ? page : NULL;
 }
 #endif /* CONFIG_ELF_CORE */
 
-- 
2.28.0.297.g1956fa8f8d-goog


  parent reply	other threads:[~2020-08-26 15:16 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-26 15:14 [PATCH v4 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_lock properly in there Jann Horn
2020-08-26 15:14 ` [PATCH v4 1/5] binfmt_elf_fdpic: Stop using dump_emit() on user pointers on !MMU Jann Horn
2020-08-26 15:14 ` [PATCH v4 2/5] coredump: Let dump_emit() bail out on short writes Jann Horn
2020-08-26 15:14 ` [PATCH v4 3/5] coredump: Refactor page range dumping into common helper Jann Horn
2020-08-26 15:14 ` [PATCH v4 4/5] binfmt_elf, binfmt_elf_fdpic: Use a VMA list snapshot Jann Horn
2020-08-26 17:14   ` Linus Torvalds
2020-08-26 15:14 ` Jann Horn [this message]
2020-08-26 17:15 ` [PATCH v4 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_lock properly in there Linus Torvalds

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