Shiyang Ruan wrote: > ==== > Changes since v13: > 1. don't return error if _freeze(FREEZE_HOLDER_KERNEL) got other error > ==== > > Now, if we suddenly remove a PMEM device(by calling unbind) which > contains FSDAX while programs are still accessing data in this device, > e.g.: > ``` > $FSSTRESS_PROG -d $SCRATCH_MNT -n 99999 -p 4 & > # $FSX_PROG -N 1000000 -o 8192 -l 500000 $SCRATCH_MNT/t001 & > echo "pfn1.1" > /sys/bus/nd/drivers/nd_pmem/unbind > ``` > it could come into an unacceptable state: > 1. device has gone but mount point still exists, and umount will fail > with "target is busy" > 2. programs will hang and cannot be killed > 3. may crash with NULL pointer dereference Thanks, this addresses my main concern that this new capability is needed otherwise DAX regresses the survivability of the kernel when removing a device from underneath the mounted filesystem compared to removing a non-DAX capable block device. > > To fix this, we introduce a MF_MEM_PRE_REMOVE flag to let it know that we > are going to remove the whole device, and make sure all related processes > could be notified so that they could end up gracefully. > > 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 > 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() > -> kill_dax() > -> dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_PRE_REMOVE) > -> xfs_dax_notify_failure() > `-> freeze_super() // freeze (kernel call) > `-> do xfs rmap > ` -> mf_dax_kill_procs() > ` -> collect_procs_fsdax() // all associated processes > ` -> unmap_and_kill() > ` -> invalidate_inode_pages2_range() // drop file's cache > `-> thaw_super() // thaw (both kernel & user call) > > Introduce MF_MEM_PRE_REMOVE to let filesystem know this is a remove > event. Use the exclusive freeze/thaw[2] to lock the filesystem to prevent > new dax mapping from being created. Do not shutdown filesystem directly > if configuration is not supported, or if failure range includes metadata > area. Make sure all files and processes(not only the current progress) > are handled correctly. Also drop the cache of associated files before > pmem is removed. > > [1]: https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > [2]: https://lore.kernel.org/linux-xfs/169116275623.3187159.16862410128731457358.stg-ugh@frogsfrogsfrogs/ I only have some questions and comment suggestions below, but otherwise consider this: Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx> > > Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx> > --- > drivers/dax/super.c | 3 +- > fs/xfs/xfs_notify_failure.c | 99 ++++++++++++++++++++++++++++++++++--- > include/linux/mm.h | 1 + > mm/memory-failure.c | 17 +++++-- > 4 files changed, 109 insertions(+), 11 deletions(-) > > diff --git a/drivers/dax/super.c b/drivers/dax/super.c > index 0da9232ea175..f4b635526345 100644 > --- a/drivers/dax/super.c > +++ b/drivers/dax/super.c > @@ -326,7 +326,8 @@ 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 4a9bbd3fe120..79586abc75bf 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; > @@ -73,10 +74,16 @@ xfs_dax_failure_fn( > struct xfs_mount *mp = cur->bc_mp; > struct xfs_inode *ip; > struct xfs_failure_info *notify = data; > + struct address_space *mapping; > + pgoff_t pgoff; > + unsigned long pgcnt; > int error = 0; > > if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) || > (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK))) { > + /* Continue the query because this isn't a failure. */ > + if (notify->mf_flags & MF_MEM_PRE_REMOVE) > + return 0; > notify->want_shutdown = true; > return 0; > } > @@ -92,14 +99,60 @@ xfs_dax_failure_fn( > return 0; > } > > - error = mf_dax_kill_procs(VFS_I(ip)->i_mapping, > - xfs_failure_pgoff(mp, rec, notify), > - xfs_failure_pgcnt(mp, rec, notify), > - notify->mf_flags); > + mapping = VFS_I(ip)->i_mapping; > + pgoff = xfs_failure_pgoff(mp, rec, notify); > + pgcnt = xfs_failure_pgcnt(mp, rec, notify); > + > + /* Continue the rmap query if the inode isn't a dax file. */ > + if (dax_mapping(mapping)) > + error = mf_dax_kill_procs(mapping, pgoff, pgcnt, > + notify->mf_flags); > + > + /* Invalidate the cache in dax pages. */ > + if (notify->mf_flags & MF_MEM_PRE_REMOVE) > + invalidate_inode_pages2_range(mapping, pgoff, > + pgoff + pgcnt - 1); > + > xfs_irele(ip); > return error; > } > > +static int > +xfs_dax_notify_failure_freeze( > + struct xfs_mount *mp) > +{ > + struct super_block *sb = mp->m_super; > + int error; > + > + error = freeze_super(sb, FREEZE_HOLDER_KERNEL); > + if (error) > + xfs_emerg(mp, "already frozen by kernel, err=%d", error); > + > + return error; > +} > + > +static void > +xfs_dax_notify_failure_thaw( > + struct xfs_mount *mp, > + bool kernel_frozen) > +{ > + struct super_block *sb = mp->m_super; > + int error; > + > + if (kernel_frozen) { > + error = thaw_super(sb, FREEZE_HOLDER_KERNEL); > + if (error) > + xfs_emerg(mp, "still frozen after notify failure, err=%d", > + error); > + } > + > + /* > + * Also thaw userspace call anyway because the device is about to be > + * removed immediately. > + */ > + thaw_super(sb, FREEZE_HOLDER_USERSPACE); I don't understand why this is not paired with a freeze in xfs_dax_notify_failure_freeze()? > +} > + > static int > xfs_dax_notify_ddev_failure( > struct xfs_mount *mp, > @@ -112,15 +165,29 @@ xfs_dax_notify_ddev_failure( > struct xfs_btree_cur *cur = NULL; > struct xfs_buf *agf_bp = NULL; > int error = 0; > + bool kernel_frozen = false; > xfs_fsblock_t fsbno = XFS_DADDR_TO_FSB(mp, daddr); > xfs_agnumber_t agno = XFS_FSB_TO_AGNO(mp, fsbno); > xfs_fsblock_t end_fsbno = XFS_DADDR_TO_FSB(mp, > daddr + bblen - 1); > xfs_agnumber_t end_agno = XFS_FSB_TO_AGNO(mp, end_fsbno); > > + if (mf_flags & MF_MEM_PRE_REMOVE) { > + xfs_info(mp, "Device is about to be removed!"); > + /* > + * Freeze fs to prevent new mappings from being created. > + * - Keep going on if others already hold the kernel forzen. > + * - Keep going on if other errors too because this device is > + * starting to fail. > + * - If kernel frozen state is hold successfully here, thaw it > + * here as well at the end. > + */ > + kernel_frozen = xfs_dax_notify_failure_freeze(mp) == 0; > + } > + > error = xfs_trans_alloc_empty(mp, &tp); > if (error) > - return error; > + goto out; > > for (; agno <= end_agno; agno++) { > struct xfs_rmap_irec ri_low = { }; > @@ -165,11 +232,23 @@ xfs_dax_notify_ddev_failure( > } > > xfs_trans_cancel(tp); > + > + /* > + * Determine how to shutdown the filesystem according to the > + * error code and flags. > + */ This comment is not adding any value. It would be better if it clarified why why want_shutdown will be false in the pre-remove case? > if (error || notify.want_shutdown) { > xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK); > if (!error) > error = -EFSCORRUPTED; > - } > + } else if (mf_flags & MF_MEM_PRE_REMOVE) > + xfs_force_shutdown(mp, SHUTDOWN_FORCE_UMOUNT); > + > +out: > + /* Thaw the fs if it is frozen before. */ > + if (mf_flags & MF_MEM_PRE_REMOVE) > + xfs_dax_notify_failure_thaw(mp, kernel_frozen); > + > return error; > } > > @@ -197,6 +276,8 @@ xfs_dax_notify_failure( > > if (mp->m_logdev_targp && mp->m_logdev_targp->bt_daxdev == dax_dev && > mp->m_logdev_targp != mp->m_ddev_targp) { Maybe a comment: /* * In the pre-remove case the failure notification is attempting to * trigger a force unmount, the expectation is that the device is still * present, but its removal is in progress and can not be cancelled, * proceed with accessing the log device. */ > + if (mf_flags & MF_MEM_PRE_REMOVE) > + return 0; > xfs_err(mp, "ondisk log corrupt, shutting down fs!"); > xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK); > return -EFSCORRUPTED; > @@ -210,6 +291,12 @@ xfs_dax_notify_failure( > ddev_start = mp->m_ddev_targp->bt_dax_part_off; > ddev_end = ddev_start + bdev_nr_bytes(mp->m_ddev_targp->bt_bdev) - 1; > > + /* Notify failure on the whole device. */ > + if (offset == 0 && len == U64_MAX) { > + offset = ddev_start; > + len = bdev_nr_bytes(mp->m_ddev_targp->bt_bdev); > + } > + > /* Ignore the range out of filesystem area */ > if (offset + len - 1 < ddev_start) > return -ENXIO; > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 2dd73e4f3d8e..a10c75bebd6d 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -3665,6 +3665,7 @@ enum mf_flags { > MF_UNPOISON = 1 << 4, > MF_SW_SIMULATED = 1 << 5, > MF_NO_RETRY = 1 << 6, > + MF_MEM_PRE_REMOVE = 1 << 7, > }; > int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index, > unsigned long count, int mf_flags); > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index e245191e6b04..e71616ccc643 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -683,7 +683,7 @@ static void add_to_kill_fsdax(struct task_struct *tsk, struct page *p, > */ > static void collect_procs_fsdax(struct page *page, > struct address_space *mapping, pgoff_t pgoff, > - struct list_head *to_kill) > + struct list_head *to_kill, bool pre_remove) > { > struct vm_area_struct *vma; > struct task_struct *tsk; > @@ -691,8 +691,15 @@ static void collect_procs_fsdax(struct page *page, > i_mmap_lock_read(mapping); > read_lock(&tasklist_lock); > for_each_process(tsk) { > - struct task_struct *t = task_early_kill(tsk, true); > + struct task_struct *t = tsk; > > + /* > + * Search for all tasks while MF_MEM_PRE_REMOVE is set, because > + * the current may not be the one accessing the fsdax page. > + * Otherwise, search for the current task. > + */ > + if (!pre_remove) > + t = task_early_kill(tsk, true); > if (!t) > continue; > vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) { > @@ -1788,6 +1795,7 @@ int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index, > dax_entry_t cookie; > struct page *page; > size_t end = index + count; > + bool pre_remove = mf_flags & MF_MEM_PRE_REMOVE; > > mf_flags |= MF_ACTION_REQUIRED | MF_MUST_KILL; > > @@ -1799,9 +1807,10 @@ int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index, > if (!page) > goto unlock; > > - SetPageHWPoison(page); > + if (!pre_remove) > + SetPageHWPoison(page); This problably wants a comment like: /* * The pre_remove case is revoking access, the memory is still good and * could theoretically be put back into service */ > > - collect_procs_fsdax(page, mapping, index, &to_kill); > + collect_procs_fsdax(page, mapping, index, &to_kill, pre_remove); > unmap_and_kill(&to_kill, page_to_pfn(page), mapping, > index, mf_flags); > unlock: > -- > 2.41.0 >
