On Tue, Sep 20, 2022 at 12:45:19PM +1000, Dave Chinner wrote: > On Fri, Sep 02, 2022 at 10:36:01AM +0000, Shiyang Ruan wrote: > > This patch is inspired by Dan's "mm, dax, pmem: Introduce > > dev_pagemap_failure()"[1]. With the help of dax_holder and > > ->notify_failure() mechanism, the pmem driver is able to ask filesystem > > (or mapped device) on it to unmap all files in use and notify processes > > who are using those files. > > > > Call trace: > > trigger unbind > > -> unbind_store() > > -> ... (skip) > > -> devres_release_all() # was pmem driver ->remove() in v1 > > -> kill_dax() > > -> dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_PRE_REMOVE) > > -> xfs_dax_notify_failure() > > > > Introduce MF_MEM_PRE_REMOVE to let filesystem know this is a remove > > event. So do not shutdown filesystem directly if something not > > supported, or if failure range includes metadata area. Make sure all > > files and processes are handled correctly. > > > > [1]: > > https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.st...@dwillia2-desk3.amr.corp.intel.com/ > > > > Signed-off-by: Shiyang Ruan <ruansy.f...@fujitsu.com> > > --- > > drivers/dax/super.c | 3 ++- > > fs/xfs/xfs_notify_failure.c | 23 +++++++++++++++++++++++ > > include/linux/mm.h | 1 + > > 3 files changed, 26 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/dax/super.c b/drivers/dax/super.c > > index 9b5e2a5eb0ae..cf9a64563fbe 100644 > > --- a/drivers/dax/super.c > > +++ b/drivers/dax/super.c > > @@ -323,7 +323,8 @@ void kill_dax(struct dax_device *dax_dev) > > return; > > > > if (dax_dev->holder_data != NULL) > > - dax_holder_notify_failure(dax_dev, 0, U64_MAX, 0); > > + dax_holder_notify_failure(dax_dev, 0, U64_MAX, > > + MF_MEM_PRE_REMOVE); > > > > clear_bit(DAXDEV_ALIVE, &dax_dev->flags); > > synchronize_srcu(&dax_srcu); > > diff --git a/fs/xfs/xfs_notify_failure.c b/fs/xfs/xfs_notify_failure.c > > index 3830f908e215..5e04ba7fa403 100644 > > --- a/fs/xfs/xfs_notify_failure.c > > +++ b/fs/xfs/xfs_notify_failure.c > > @@ -22,6 +22,7 @@ > > > > #include <linux/mm.h> > > #include <linux/dax.h> > > +#include <linux/fs.h> > > > > struct xfs_failure_info { > > xfs_agblock_t startblock; > > @@ -77,6 +78,9 @@ xfs_dax_failure_fn( > > > > if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) || > > (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK))) { > > + /* The device is about to be removed. Not a really failure. */ > > + if (notify->mf_flags & MF_MEM_PRE_REMOVE) > > + return 0; > > notify->want_shutdown = true; > > return 0; > > } > > @@ -182,12 +186,23 @@ xfs_dax_notify_failure( > > struct xfs_mount *mp = dax_holder(dax_dev); > > u64 ddev_start; > > u64 ddev_end; > > + int error; > > > > if (!(mp->m_super->s_flags & SB_BORN)) { > > xfs_warn(mp, "filesystem is not ready for notify_failure()!"); > > return -EIO; > > } > > > > + if (mf_flags & MF_MEM_PRE_REMOVE) { > > + xfs_info(mp, "device is about to be removed!"); > > + down_write(&mp->m_super->s_umount); > > + error = sync_filesystem(mp->m_super); > > + drop_pagecache_sb(mp->m_super, NULL); > > + up_write(&mp->m_super->s_umount); > > + if (error) > > + return error; > > If the device is about to go away unexpectedly, shouldn't this shut > down the filesystem after syncing it here? If the filesystem has > been shut down, then everything will fail before removal finally > triggers, and the act of unmounting the filesystem post device > removal will clean up the page cache and all the other caches.
IIRC they want to kill all the processes with MAP_SYNC mappings sooner than whenever the admin gets around to unmounting the filesystem, which is why PRE_REMOVE will then go walk the rmapbt to find processes to shoot down. I'm not sure, though, if drop_pagecache_sb only touches DRAM page cache or if it'll shoot down fsdax mappings too? > IOWs, I don't understand why the page cache is considered special > here (as opposed to, say, the inode or dentry caches), nor why we > aren't shutting down the filesystem directly after syncing it to > disk to ensure that we don't end up with applications losing data as > a result of racing with the removal.... But yeah, we might as well shut down the fs at the end of PRE_REMOVE handling, if the rmap walk hasn't already done that. --D > Cheers, > > Dave. > -- > Dave Chinner > da...@fromorbit.com
