The patch titled
Subject: mm: hold the RCU read lock over calls to ->map_pages
has been added to the -mm mm-unstable branch. Its filename is
mm-hold-the-rcu-read-lock-over-calls-to-map_pages.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hold-the-rcu-read-lock-over-calls-to-map_pages.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Subject: mm: hold the RCU read lock over calls to ->map_pages
Date: Mon, 27 Mar 2023 18:45:15 +0100
Prevent filesystems from doing things which sleep in their map_pages
method. This is in preparation for a pagefault path protected only by
RCU.
Link: https://lkml.kernel.org/r/20230327174515.1811532-4-willy@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Darrick J. Wong <djwong@xxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/locking.rst | 4 ++--
mm/memory.c | 11 ++++++++---
2 files changed, 10 insertions(+), 5 deletions(-)
--- a/Documentation/filesystems/locking.rst~mm-hold-the-rcu-read-lock-over-calls-to-map_pages
+++ a/Documentation/filesystems/locking.rst
@@ -645,7 +645,7 @@ ops mmap_lock PageLocked(page)
open: yes
close: yes
fault: yes can return with page locked
-map_pages: yes
+map_pages: read
page_mkwrite: yes can return with page locked
pfn_mkwrite: yes
access: yes
@@ -661,7 +661,7 @@ locked. The VM will unlock the page.
->map_pages() is called when VM asks to map easy accessible pages.
Filesystem should find and map pages associated with offsets from "start_pgoff"
-till "end_pgoff". ->map_pages() is called with page table locked and must
+till "end_pgoff". ->map_pages() is called with the RCU lock held and must
not block. If it's not possible to reach a page without blocking,
filesystem should skip it. Filesystem should use do_set_pte() to setup
page table entry. Pointer to entry associated with the page is passed in
--- a/mm/memory.c~mm-hold-the-rcu-read-lock-over-calls-to-map_pages
+++ a/mm/memory.c
@@ -4459,6 +4459,7 @@ static vm_fault_t do_fault_around(struct
/* The page offset of vmf->address within the VMA. */
pgoff_t vma_off = vmf->pgoff - vmf->vma->vm_pgoff;
pgoff_t from_pte, to_pte;
+ vm_fault_t ret;
/* The PTE offset of the start address, clamped to the VMA. */
from_pte = max(ALIGN_DOWN(pte_off, nr_pages),
@@ -4474,9 +4475,13 @@ static vm_fault_t do_fault_around(struct
return VM_FAULT_OOM;
}
- return vmf->vma->vm_ops->map_pages(vmf,
- vmf->pgoff + from_pte - pte_off,
- vmf->pgoff + to_pte - pte_off);
+ rcu_read_lock();
+ ret = vmf->vma->vm_ops->map_pages(vmf,
+ vmf->pgoff + from_pte - pte_off,
+ vmf->pgoff + to_pte - pte_off);
+ rcu_read_unlock();
+
+ return ret;
}
/* Return true if we should do read fault-around, false otherwise */
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxx are
xfs-remove-xfs_filemap_map_pages-wrapper.patch
afs-split-afs_pagecache_valid-out-of-afs_validate.patch
mm-hold-the-rcu-read-lock-over-calls-to-map_pages.patch
