On Thu, Apr 9, 2020 at 11:30 AM Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> wrote: > > Stacked filesystems like overlayfs has no own writeback, but they have to > forward syncfs() requests to backend for keeping data integrity. > > During global sync() each overlayfs instance calls method ->sync_fs() > for backend although it itself is in global list of superblocks too. > As a result one syscall sync() could write one superblock several times > and send multiple disk barriers. > > This patch adds flag SB_I_SKIP_SYNC into sb->sb_iflags to avoid that. > > Reported-by: Dmitry Monakhov <dmtrmonakhov@xxxxxxxxxxxxxx> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> > --- Seems reasonable. You may add: Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx> +CC: containers list This bring up old memories. I posted this way back to fix handling of emergency_remount() in the presence of loop mounted fs: https://lore.kernel.org/linux-ext4/CAA2m6vfatWKS1CQFpaRbii2AXiZFvQUjVvYhGxWTSpz+2rxDyg@xxxxxxxxxxxxxx/ But seems to me that emergency_sync() and sync(2) are equally broken for this use case. I wonder if anyone cares enough about resilience of loop mounted fs to try and change the iterate_* functions to iterate supers/bdevs in reverse order... Thanks, Amir.
