Re: [PATCH 3/3] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind

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

在 2022/9/15 2:15, Darrick J. Wong 写道:
> On Fri, Sep 02, 2022 at 10:36:01AM +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()   # 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.
>>
>> [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 | 23 +++++++++++++++++++++++
>>   include/linux/mm.h          |  1 +
>>   3 files changed, 26 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 3830f908e215..5e04ba7fa403 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;
>> @@ -77,6 +78,9 @@ xfs_dax_failure_fn(
>>   
>>   	if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) ||
>>   	    (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK))) {
>> +		/* 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;
>>   	}
>> @@ -182,12 +186,23 @@ 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()!");
>>   		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);
>> +		drop_pagecache_sb(mp->m_super, NULL);
>> +		up_write(&mp->m_super->s_umount);
>> +		if (error)
>> +			return error;
>> +	}
>> +
>>   	if (mp->m_rtdev_targp && mp->m_rtdev_targp->bt_daxdev == dax_dev) {
>>   		xfs_debug(mp,
>>   			 "notify_failure() not supported on realtime device!");
>> @@ -196,6 +211,8 @@ 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 +226,12 @@ 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);
>> +	}
> 
> I wonder, won't the trimming code below take care of this?

The len is U64_MAX, so 'offset + len - 1' will overflow.  That can't be 
handled correctly by the trimming code below.


--
Thanks,
Ruan.

> 
> The rest of the patch looks ok to me.
> 
> --D
> 
>> +
>>   	/* 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 21f8b27bd9fd..9122a1c57dd2 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -3183,6 +3183,7 @@ 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);
>> -- 
>> 2.37.2
>>