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@xxxxxxxxxxxxx> --- Documentation/filesystems/locking.rst | 4 ++-- mm/memory.c | 7 ++++++- 2 files changed, 8 insertions(+), 3 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 f1cf47b7e3bb..77577a1d09ac 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4442,6 +4442,7 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) unsigned long address = vmf->address, nr_pages, mask; pgoff_t start_pgoff = vmf->pgoff; pgoff_t end_pgoff; + vm_fault_t ret; int off; nr_pages = READ_ONCE(fault_around_bytes) >> PAGE_SHIFT; @@ -4467,7 +4468,11 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) return VM_FAULT_OOM; } - return vmf->vma->vm_ops->map_pages(vmf, start_pgoff, end_pgoff); + rcu_read_lock(); + ret = vmf->vma->vm_ops->map_pages(vmf, start_pgoff, end_pgoff); + rcu_read_unlock(); + + return ret; } /* Return true if we should do read fault-around, false otherwise */ -- 2.35.1
