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. > 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 --D
