fix-enospc-handling-in-dax-page-fault-handler

   1 ext4: fix ENOSPC handling in DAX page fault handler
   2
   3 From: Jan Kara <jack@suse.cz>
   4
   5 When allocation of underlying block for a page fault fails, we fail the
   6 fault with SIGBUS. However we may well hit ENOSPC just due to lots of
   7 free blocks being held by the running / committing transaction. So
   8 propagate the error from ext4_iomap_begin() and implement do standard
   9 allocation retry loop in ext4_dax_huge_fault().
  10
  11 Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
  12 Signed-off-by: Jan Kara <jack@suse.cz>
  13 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  14 ---
  15  fs/ext4/file.c | 10 ++++++++--
  16  1 file changed, 8 insertions(+), 2 deletions(-)
  17
  18 diff --git a/fs/ext4/file.c b/fs/ext4/file.c
  19 index 1c7cd882d998..fb6f023622fe 100644
  20 --- a/fs/ext4/file.c
  21 +++ b/fs/ext4/file.c
  22 @@ -280,7 +280,8 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
  23  static int ext4_dax_huge_fault(struct vm_fault *vmf,
  24                 enum page_entry_size pe_size)
  25  {
  26 -       int result;
  27 +       int result, error = 0;
  28 +       int retries = 0;
  29         handle_t *handle = NULL;
  30         struct inode *inode = file_inode(vmf->vma->vm_file);
  31         struct super_block *sb = inode->i_sb;
  32 @@ -304,6 +305,7 @@ static int ext4_dax_huge_fault(struct vm_fault *vmf,
  33                 sb_start_pagefault(sb);
  34                 file_update_time(vmf->vma->vm_file);
  35                 down_read(&EXT4_I(inode)->i_mmap_sem);
  36 +retry:
  37                 handle = ext4_journal_start_sb(sb, EXT4_HT_WRITE_PAGE,
  38                                                EXT4_DATA_TRANS_BLOCKS(sb));
  39                 if (IS_ERR(handle)) {
  40 @@ -314,9 +316,13 @@ static int ext4_dax_huge_fault(struct vm_fault *vmf,
  41         } else {
  42                 down_read(&EXT4_I(inode)->i_mmap_sem);
  43         }
  44 -       result = dax_iomap_fault(vmf, pe_size, &pfn, NULL, &ext4_iomap_ops);
  45 +       result = dax_iomap_fault(vmf, pe_size, &pfn, &error, &ext4_iomap_ops);
  46         if (write) {
  47                 ext4_journal_stop(handle);
  48 +
  49 +               if ((result & VM_FAULT_ERROR) && error == -ENOSPC &&
  50 +                   ext4_should_retry_alloc(sb, &retries))
  51 +                       goto retry;
  52                 /* Handling synchronous page fault? */
  53                 if (result & VM_FAULT_NEEDDSYNC)
  54                         result = dax_finish_sync_fault(vmf, pe_size, pfn);
  55 --
  56 2.12.3
  57
  58