[PATCH v2 3/3] mm: Hold the RCU read lock over calls to ->map_pages
Matthew Wilcox (Oracle)
willy at infradead.org
Mon Mar 27 10:45:15 PDT 2023
Prevent filesystems from doing things which sleep in their map_pages
method. This is in preparation for a pagefault path protected only
by RCU.
Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org>
---
Documentation/filesystems/locking.rst | 4 ++--
mm/memory.c | 11 ++++++++---
2 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 922886fefb7f..8a80390446ba 100644
--- a/Documentation/filesystems/locking.rst
+++ b/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 set_pte_range() to setup
page table entry. Pointer to entry associated with the page is passed in
diff --git a/mm/memory.c b/mm/memory.c
index 8071bb17abf2..a7edf6d714db 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4461,6 +4461,7 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf)
/* 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),
@@ -4476,9 +4477,13 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf)
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 */
--
2.39.2
More information about the linux-afs
mailing list