在 2023/8/25 7:57, Darrick J. Wong 写道:
On Thu, Aug 24, 2023 at 05:41:50PM +0800, Shiyang Ruan wrote:在 2023/8/24 7:36, Darrick J. Wong 写道:On Wed, Aug 23, 2023 at 04:17:06PM +0800, Shiyang Ruan wrote:==== Changes since v12: 1. correct flag name in subject (MF_MEM_REMOVE => MF_MEM_PRE_REMOVE) 2. complete the behavior when fs has already frozen by kernel call NOTICE: Instead of "call notify_failure() again w/o PRE_REMOVE", I tried this proposal[0]. 3. call xfs_dax_notify_failure_freeze() and _thaw() in same function 4. rebase on: xfs/xfs-linux.git vfs-for-next ==== 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 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. [0]: https://lore.kernel.org/linux-xfs/25cf6700-4db0-a346-632c-ec9fc291793a@xxxxxxxxxxx/ [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/ 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 c4c4728a36e4..2e1a35e82fce 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 4a9bbd3fe120..6496c32a9172 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.Does a userspace freeze inhibit or otherwise break device removal?It doesn't. Device can be removed. But after that, the mount point still exists, and `umount /mnt/scratch` fails with "target is busy." `xfs_freeze -u /mnt/scratch` cannot work too.Yes, that's true, but that's long been the case for removing block devices. Should block device removal (since we now have hooks for that!) also be breaking freezes?
I think so. But it may need more time to accomplish. Shall we leave it for later optimization?
So, I think thaw_super() anyway here is needed.+ */ + thaw_super(sb, FREEZE_HOLDER_USERSPACE); +} + 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. */ + error = xfs_dax_notify_failure_freeze(mp); + if (error) { + /* Keep going on if filesystem is frozen by kernel. */ + if (error == -EBUSY) + kernel_frozen = true;EBUSY means that xfs_dax_notify_failure_freeze did /not/ succeed in kernel-freezing the fs. Someone else did, and they're expecting that thaw_super will undo that. switch (error) { case -EBUSY: /* someone else froze the fs, keep going */ break; case 0: /* we froze the fs */ kernel_frozen = true; break; default: /* something else broke, should we continue anyway? */ return error; } TBH I wonder why all that isn't just: kernel_frozen = xfs_dax_notify_failure_freeze(mp) == 0; Since we'd want to keep going even if (say) the pmem was already starting to fail and the freeze actually failed due to EIO, right?Yes. So we can say it is a *try* to _freeze() here. No matter what its result is, we continue. Then I think the `kernel_frozen` becomes useless as well. Because we should try to call both _thaw(KERNEL_CALL) and _thaw(USER_CALL) to make sure umount can work after device is gone.I disagree -- unlike the mess that is userspace freezing, kernel code that obtained a kernel freeze will get very confused and potentially do Seriously Bad Things if the kernel freeze is yanked out from under them. Kernel code is not supposed to release things that they did not themselves obtain. That might not ultimately matter for the narrow case of the device going away, but the two other usecases (online fsck and suspend) will malfunction if you drop a kernel freeze that they obtained.
Could online fsck and suspend keep working even after `xfs_force_shutdown(mp, SHUTDOWN_FORCE_UMOUNT);` being called?
I don't mind if PREREMOVE can't get a freeze and keeps going with the invalidations anyway. We did our best, and when the pmem goes away we can just kill -9 down the processes.
Ok, I agree. Then, the last thing I want to be confirmed:On my host, if the freeze state wasn't _thaw() after device gone, the processes will keep on waiting and cannot be killed by `kill -9` manually. Is there another way to make the processes killed?
-- Thanks, Ruan.
--DThen, I think it's better to change them: `static int xfs_dax_notify_failure_freeze()`, `static void xfs_dax_notify_failure_thaw()` to `static void xfs_dax_notify_failure_try_freeze()`, `static void xfs_dax_notify_failure_try_thaw()`. -- Thanks, Ruan.--D+ else + return error; + } + } + 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. + */ 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) { + 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 799836e84840..944a1165a321 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3577,6 +3577,7 @@ 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 dc5ff7dd4e50..92f18c9e0aaf 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -688,7 +688,7 @@ 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; @@ -696,8 +696,15 @@ 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) { @@ -1793,6 +1800,7 @@ 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; @@ -1804,9 +1812,10 @@ int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index, if (!page) goto unlock; - SetPageHWPoison(page); + if (!pre_remove) + SetPageHWPoison(page); - 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
