On Tue, 2017-10-10 at 15:30 -0700, Shaohua Li wrote: > On Tue, Oct 10, 2017 at 02:03:39PM -0700, Bart Van Assche wrote: > > Some people use the md driver on laptops and use the suspend and > > resume functionality. Since it is essential that submitting of > > new I/O requests stops before a hibernation image is created, > > interrupt the md resync and reshape actions if the system is > > being frozen. Note: the resync and reshape will restart after > > the system is resumed and a message similar to the following > > will appear in the system log: > > > > md: md0: data-check interrupted. > > Where do we restart resync and reshape? Hello Shaohua, My understanding of the md driver is as follows: - Before any write occurs, md_write_start() is called. That function clears mddev->safemode and checks mddev->in_sync. If that variable is set, it is cleared and md_write_start() wakes up mddev->thread and waits until the superblock has been written to disk. - All mddev->thread implementations call md_check_recovery(). That function updates the superblock by calling md_update_sb() if needed. md_check_recovery() also starts a resync thread if the array is not in sync. See also the comment block above md_check_recovery(). - md_do_sync() performs the resync. If it completes successfully the "in_sync" state is set (set_in_sync()). If it is interrupted the "in_sync" state is not modified. - super_90_sync() sets the MD_SB_CLEAN flag in the on-disk superblock if the "in_sync" flag is set. In other words: if the array is in sync the MD_SB_CLEAN flag is set in the on-disk superblock. If a resync is needed that flag is not set. The MD_SB_CLEAN flag is checked when the superblock is loaded. If that flag is not set a resync is started. Bart.
