From: Jan Kara <jack@xxxxxxx> Subject: ext4: return to starting transaction in ext4_dax_huge_fault() DAX will return to locking exceptional entry before mapping blocks for a page fault to fix possible races with concurrent writes. To avoid lock inversion between exceptional entry lock and transaction start, start the transaction already in ext4_dax_huge_fault(). Fixes: 9f141d6ef6258a3a37a045842d9ba7e68f368956 Link: http://lkml.kernel.org/r/20170510085419.27601-4-jack@xxxxxxx Signed-off-by: Jan Kara <jack@xxxxxxx> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/ext4/file.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff -puN fs/ext4/file.c~ext4-return-back-to-starting-transaction-in-ext4_dax_huge_fault fs/ext4/file.c --- a/fs/ext4/file.c~ext4-return-back-to-starting-transaction-in-ext4_dax_huge_fault +++ a/fs/ext4/file.c @@ -257,6 +257,7 @@ static int ext4_dax_huge_fault(struct vm enum page_entry_size pe_size) { int result; + handle_t *handle = NULL; struct inode *inode = file_inode(vmf->vma->vm_file); struct super_block *sb = inode->i_sb; bool write = vmf->flags & FAULT_FLAG_WRITE; @@ -264,12 +265,24 @@ static int ext4_dax_huge_fault(struct vm if (write) { sb_start_pagefault(sb); file_update_time(vmf->vma->vm_file); + down_read(&EXT4_I(inode)->i_mmap_sem); + handle = ext4_journal_start_sb(sb, EXT4_HT_WRITE_PAGE, + EXT4_DATA_TRANS_BLOCKS(sb)); + } else { + down_read(&EXT4_I(inode)->i_mmap_sem); } - down_read(&EXT4_I(inode)->i_mmap_sem); - result = dax_iomap_fault(vmf, pe_size, &ext4_iomap_ops); - up_read(&EXT4_I(inode)->i_mmap_sem); - if (write) + if (!IS_ERR(handle)) + result = dax_iomap_fault(vmf, pe_size, &ext4_iomap_ops); + else + result = VM_FAULT_SIGBUS; + if (write) { + if (!IS_ERR(handle)) + ext4_journal_stop(handle); + up_read(&EXT4_I(inode)->i_mmap_sem); sb_end_pagefault(sb); + } else { + up_read(&EXT4_I(inode)->i_mmap_sem); + } return result; } _