在 2022/7/19 6:56, Dan Williams 写道: > 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. Hi Dan, Darrick Do I need to fix somewhere on this patch? I'm not sure if it is looked good... -- Thanks, Ruan. > >> >>> 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.
