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If an ext4 filesystem is mounted with both the DAX and read-only options, executables on that filesystem will fail to start (claiming 'Segmentation fault') due to the fault handler returning VM_FAULT_SIGBUS. This is due to the DAX fault handler (see ext4_dax_huge_fault) attempting to write to the journal when FAULT_FLAG_WRITE is set. This is the wrong behavior for write faults which will lead to a COW page; in particular, this fails for readonly mounts. This change avoids journal writes for faults that are expected to COW. It might be the case that this could be better handled in ext4_iomap_begin / ext4_iomap_end (called via iomap_ops inside dax_iomap_fault). These is some overlap already (e.g. grabbing journal handles). Signed-off-by: Randy Dodgen <dodgen@google.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.