On Tue, Jan 20, 2015 at 12:21:37PM +0100, Jan Kara wrote: > On Mon 19-01-15 22:07:01, Namjae Jeon wrote: > > > > When this state is set, any process which tries to modify the file's address > > > > space, either by pagefault mmap writes or using write(2), will block until > > > > the this state is cleared. I_WRITE_FREEZED is set by calling FS_IOC_FWFREEZE > > > > ioctl and clear by FS_IOC_FWTHAW ioctl. .... > > I checked the routines where checks for I_FROZEN would be required. > > Most of them are Ok but do_unlinkat() confuses me a little. > > vfs_unlink is called under parent inode's i_mutex, so we cannot sleep > > keeping parent's i_mutex held. > > i.e while freezing file, all file in directory are blocked by parent > > i_mutex. Is it ok to release parnets->mutex before checking for I_FROZEN > > or there is some idea? > So I believe Dave thought that you'd just reuse places we currently use > to call sb_start_write() / mnt_want_write(). You'd probably have to come up > with a function like path_want_write() (takes struct path as an argument) > and which will call mnt_want_write(), sb_start_write(), and do appropriate > inode freeze handling. Then you replace all calls to mnt_want_write() with > calls to path_want_write()... Possibly you can also provide a trivial > wrapper for path_want_write() which takes struct file instead. Yes, that's pretty much what I as thinking - a single function that does all the freeze checking/blocking for a given operation, regardless of the type of freeze we block on. That way all the nesting semantics are located in one set of code, and it's easy to verify correct. > This should also deal with the locking problems you describe above as > mnt_want_write() is always called before taking i_mutex. *nod* Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
