Darrick J. Wong wrote: > On Thu, Jul 14, 2022 at 11:21:44AM -0700, Dan Williams wrote: > > ruansy.fnst@xxxxxxxxxxx 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. > > > > > > == > > > Changes since v5: > > > 1. Renamed MF_MEM_REMOVE to MF_MEM_PRE_REMOVE > > > 2. hold s_umount before sync_filesystem() > > > 3. move sync_filesystem() after SB_BORN check > > > 4. Rebased on next-20220714 > > > > > > Changes since v4: > > > 1. sync_filesystem() at the beginning when MF_MEM_REMOVE > > > 2. Rebased on next-20220706 > > > > > > [1]: https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > > > > > Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx> > > > --- > > > drivers/dax/super.c | 3 ++- > > > fs/xfs/xfs_notify_failure.c | 15 +++++++++++++++ > > > include/linux/mm.h | 1 + > > > 3 files changed, 18 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 69d9c83ea4b2..6da6747435eb 100644 > > > --- a/fs/xfs/xfs_notify_failure.c > > > +++ b/fs/xfs/xfs_notify_failure.c > > > @@ -76,6 +76,9 @@ xfs_dax_failure_fn( > > > > > > if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) || > > > (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK))) { > > > + /* Do not shutdown so early when device is to be removed */ > > > + if (notify->mf_flags & MF_MEM_PRE_REMOVE) > > > + return 0; > > > xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK); > > > return -EFSCORRUPTED; > > > } > > > @@ -174,12 +177,22 @@ xfs_dax_notify_failure( > > > struct xfs_mount *mp = dax_holder(dax_dev); > > > u64 ddev_start; > > > u64 ddev_end; > > > + int error; > > > > > > if (!(mp->m_sb.sb_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); > > > + up_write(&mp->m_super->s_umount); > > > > Are all mappings invalidated after this point? > > No; all this step does is pushes dirty filesystem [meta]data to pmem > before we lose DAXDEV_ALIVE... > > > The goal of the removal notification is to invalidate all DAX mappings > > that are no pointing to pfns that do not exist anymore, so just syncing > > does not seem like enough, and the shutdown is skipped above. What am I > > missing? > > ...however, the shutdown above only applies to filesystem metadata. In > effect, we avoid the fs shutdown in MF_MEM_PRE_REMOVE mode, which > enables the mf_dax_kill_procs calls to proceed against mapped file data. > I have a nagging suspicion that in non-PREREMOVE mode, we can end up > shutting down the filesytem on an xattr block and the 'return > -EFSCORRUPTED' actually prevents us from reaching all the remaining file > data mappings. > > IOWs, I think that clause above really ought to have returned zero so > that we keep the filesystem up while we're tearing down mappings, and > only call xfs_force_shutdown() after we've had a chance to let > xfs_dax_notify_ddev_failure() tear down all the mappings. > > I missed that subtlety in the initial ~30 rounds of review, but I figure > at this point let's just land it in 5.20 and clean up that quirk for > -rc1. Sure, this is a good baseline to incrementally improve. > > > Notice that kill_dev_dax() does unmap_mapping_range() after invalidating > > the dax device and that ensures that all existing mappings are gone and > > cannot be re-established. As far as I can see a process with an existing > > dax mapping will still be able to use it after this runs, no? > > I'm not sure where in akpm's tree I find kill_dev_dax()? I'm cribbing > off of: > > https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/tree/fs/xfs/xfs_notify_failure.c?h=mm-stable https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/tree/drivers/dax/bus.c?h=mm-stable#n381 Where the observation is that when device-dax is told that the device is going away it invalidates all the active mappings to that single character-device-inode. The hope being that in the fsdax case all the dax-mapped filesystem inodes would experience the same irreversible invalidation as the device is exiting.
