mm: drop mmap_sem before calling balance_dirty_pages() in write fault

One of our services is observing hanging ps/top/etc under heavy write
IO, and the task states show this is an mmap_sem priority inversion:

A write fault is holding the mmap_sem in read-mode and waiting for
(heavily cgroup-limited) IO in balance_dirty_pages():

    balance_dirty_pages+0x724/0x905
    balance_dirty_pages_ratelimited+0x254/0x390
    fault_dirty_shared_page.isra.96+0x4a/0x90
    do_wp_page+0x33e/0x400
    __handle_mm_fault+0x6f0/0xfa0
    handle_mm_fault+0xe4/0x200
    __do_page_fault+0x22b/0x4a0
    page_fault+0x45/0x50

Somebody tries to change the address space, contending for the mmap_sem in
write-mode:

    call_rwsem_down_write_failed_killable+0x13/0x20
    do_mprotect_pkey+0xa8/0x330
    SyS_mprotect+0xf/0x20
    do_syscall_64+0x5b/0x100
    entry_SYSCALL_64_after_hwframe+0x3d/0xa2

The waiting writer locks out all subsequent readers to avoid lock
starvation, and several threads can be seen hanging like this:

    call_rwsem_down_read_failed+0x14/0x30
    proc_pid_cmdline_read+0xa0/0x480
    __vfs_read+0x23/0x140
    vfs_read+0x87/0x130
    SyS_read+0x42/0x90
    do_syscall_64+0x5b/0x100
    entry_SYSCALL_64_after_hwframe+0x3d/0xa2

To fix this, do what we do for cache read faults already: drop the
mmap_sem before calling into anything IO bound, in this case the
balance_dirty_pages() function, and return VM_FAULT_RETRY.

Link: http://lkml.kernel.org/r/20190924194238.GA29030@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 27 insertions, 11 deletions

diff --git a/mm/memory.c b/mm/memory.c
index b6a5d6a08438..9ea917e28ef4 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2289,10 +2289,11 @@ static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
  *
  * The function expects the page to be locked and unlocks it.
  */
-static void fault_dirty_shared_page(struct vm_area_struct *vma,
-				    struct page *page)
+static vm_fault_t fault_dirty_shared_page(struct vm_fault *vmf)
 {
+	struct vm_area_struct *vma = vmf->vma;
 	struct address_space *mapping;
+	struct page *page = vmf->page;
 	bool dirtied;
 	bool page_mkwrite = vma->vm_ops && vma->vm_ops->page_mkwrite;
 
@@ -2307,16 +2308,30 @@ static void fault_dirty_shared_page(struct vm_area_struct *vma,
 	mapping = page_rmapping(page);
 	unlock_page(page);
 
+	if (!page_mkwrite)
+		file_update_time(vma->vm_file);
+
+	/*
+	 * Throttle page dirtying rate down to writeback speed.
+	 *
+	 * mapping may be NULL here because some device drivers do not
+	 * set page.mapping but still dirty their pages
+	 *
+	 * Drop the mmap_sem before waiting on IO, if we can. The file
+	 * is pinning the mapping, as per above.
+	 */
 	if ((dirtied || page_mkwrite) && mapping) {
-		/*
-		 * Some device drivers do not set page.mapping
-		 * but still dirty their pages
-		 */
+		struct file *fpin;
+
+		fpin = maybe_unlock_mmap_for_io(vmf, NULL);
 		balance_dirty_pages_ratelimited(mapping);
+		if (fpin) {
+			fput(fpin);
+			return VM_FAULT_RETRY;
+		}
 	}
 
-	if (!page_mkwrite)
-		file_update_time(vma->vm_file);
+	return 0;
 }
 
 /*
@@ -2571,6 +2586,7 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf)
 	__releases(vmf->ptl)
 {
 	struct vm_area_struct *vma = vmf->vma;
+	vm_fault_t ret = VM_FAULT_WRITE;
 
 	get_page(vmf->page);
 
@@ -2594,10 +2610,10 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf)
 		wp_page_reuse(vmf);
 		lock_page(vmf->page);
 	}
-	fault_dirty_shared_page(vma, vmf->page);
+	ret |= fault_dirty_shared_page(vmf);
 	put_page(vmf->page);
 
-	return VM_FAULT_WRITE;
+	return ret;
 }
 
 /*
@@ -3641,7 +3657,7 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf)
 		return ret;
 	}
 
-	fault_dirty_shared_page(vma, vmf->page);
+	ret |= fault_dirty_shared_page(vmf);
 	return ret;
 }