Re: [PATCH v11 2/2] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind

[Shiyang Ruan <ruansy.fnst@fujitsu.com>]

在 2023/4/5 1:45, Darrick J. Wong 写道:
> On Tue, Mar 28, 2023 at 09:41:46AM +0000, Shiyang Ruan 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()
>>      -> kill_dax()
>>       -> dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_PRE_REMOVE)
>>        -> xfs_dax_notify_failure()
>>        `-> freeze_super()
>>        `-> do xfs rmap
>>        ` -> mf_dax_kill_procs()
>>        `  -> collect_procs_fsdax()    // all associated
>>        `  -> unmap_and_kill()
>>        ` -> invalidate_inode_pages2() // drop file's cache
>>        `-> thaw_super()
>>
>> Introduce MF_MEM_PRE_REMOVE to let filesystem know this is a remove
>> event.  Freeze the filesystem to prevent new dax mapping being created.
>> And 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.  Also drop the cache of associated
>> files before pmem is removed.
>>
>> [1]: https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@dwillia2-desk3.amr.corp.intel.com/
>>
>> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
>> ---
>>   drivers/dax/super.c         |  3 +-
>>   fs/xfs/xfs_notify_failure.c | 56 +++++++++++++++++++++++++++++++++----
>>   include/linux/mm.h          |  1 +
>>   mm/memory-failure.c         | 17 ++++++++---
>>   4 files changed, 67 insertions(+), 10 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 1e2eddb8f90f..1b4eff43f9b5 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))) {
>> +		/* The device is about to be removed.  Not a really failure. */
>> +		if (notify->mf_flags & MF_MEM_PRE_REMOVE)
>> +			return 0;
>>   		notify->want_shutdown = true;
>>   		return 0;
>>   	}
>> @@ -92,10 +99,18 @@ 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 anyway. */
>> +	invalidate_inode_pages2_range(mapping, pgoff, pgoff + pgcnt - 1);
>> +
>>   	xfs_irele(ip);
>>   	return error;
>>   }
>> @@ -164,11 +179,25 @@ xfs_dax_notify_ddev_failure(
>>   	}
>>   
>>   	xfs_trans_cancel(tp);
>> +
>> +	/* Unfreeze filesystem anyway if it is freezed before. */
>> +	if (mf_flags & MF_MEM_PRE_REMOVE) {
>> +		error = thaw_super(mp->m_super);
>> +		if (error)
>> +			return error;
> 
> If someone *else* wanders in and thaws the fs, you'll get EINVAL here.
> 
> I guess that's useful for knowing if someone's screwed up the freeze
> state on us, but ... really, don't you want to make sure you've gotten
> the freeze and nobody else can take it away?

Ok, I know it now.
> 
> I think you want the kernel-initiated freeze proposed by Luis here:
> https://lore.kernel.org/linux-fsdevel/20230114003409.1168311-4-mcgrof@kernel.org/

This patch gives userspace higher priority to do freeze/thaw then 
kernelspace.  Userspace can thaw it even when kernelspace needs the 
freeze state.  But I think it can't happen in this case.  Kernelspace(in 
this case) should hold the freeze state and, IOW, has higher priority 
than userspace.  I think we could change the @usercall to @priority.

-int freeze_super(struct super_block *sb)
+int freeze_super(struct super_block *sb, int priority)

And priority definitions like:
#define FREEZE_PRO_AUTO           0  // for auto freeze
#define FREEZE_PRO_USERCALL       1  // for user call
#define FREEZE_PRO_KERNELCALL     2  // for kernel call


--
Thanks,
Ruan.

> 
> Also: Is Fujitsu still pursuing pmem products?  Even though Optane is
> dead?  I'm no longer sure of what the roadmap is for all this fsdax code
> and whatnot.
> 
> --D
> 
>> +	}
>> +
>> +	/*
>> +	 * 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);
>> +
>>   	return error;
>>   }
>>   
>> @@ -182,6 +211,7 @@ xfs_dax_notify_failure(
>>   	struct xfs_mount	*mp = dax_holder(dax_dev);
>>   	u64			ddev_start;
>>   	u64			ddev_end;
>> +	int			error;
>>   
>>   	if (!(mp->m_super->s_flags & SB_BORN)) {
>>   		xfs_warn(mp, "filesystem is not ready for notify_failure()!");
>> @@ -196,6 +226,8 @@ 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;
>> @@ -209,6 +241,12 @@ 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;
>> @@ -225,6 +263,14 @@ xfs_dax_notify_failure(
>>   	if (offset + len - 1 > ddev_end)
>>   		len = ddev_end - offset + 1;
>>   
>> +	if (mf_flags & MF_MEM_PRE_REMOVE) {
>> +		xfs_info(mp, "device is about to be removed!");
>> +		/* Freeze the filesystem to prevent new mappings created. */
>> +		error = freeze_super(mp->m_super);
>> +		if (error)
>> +			return error;
>> +	}
>> +
>>   	return xfs_dax_notify_ddev_failure(mp, BTOBB(offset), BTOBB(len),
>>   			mf_flags);
>>   }
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 1f79667824eb..ac3f22c20e1d 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -3436,6 +3436,7 @@ 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 fae9baf3be16..6e6acec45568 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -623,7 +623,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
>>    */
>>   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;
>> @@ -631,8 +631,15 @@ 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, 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) {
>> @@ -1732,6 +1739,7 @@ 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;
>>   
>> @@ -1743,9 +1751,10 @@ 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:
>> -- 
>> 2.39.2
>>