Re: [PATCH v3] cifs: Wait for writebacks to complete before attempting write.

[Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Tue, 11 Mar 2014 16:11:47 +0000
Sachin Prabhu <sprabhu-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:

> Problem reported in Red Hat bz 1040329 for strict writes where we cache
> only when we hold oplock and write direct to the server when we don't.
> 
> When we receive an oplock break, we first change the oplock value for
> the inode in cifsInodeInfo->oplock to indicate that we no longer hold
> the oplock before we enqueue a task to flush changes to the backing
> device. Once we have completed flushing the changes, we return the
> oplock to the server.
> 
> There are 2 ways here where we can have data corruption
> 1) While we flush changes to the backing device as part of the oplock
> break, we can have processes write to the file. These writes check for
> the oplock, find none and attempt to write directly to the server.
> These direct writes made while we are flushing from cache could be
> overwritten by data being flushed from the cache causing data
> corruption.
> 2) While a thread runs in cifs_strict_writev, the machine could receive
> and process an oplock break after the thread has checked the oplock and
> found that it allows us to cache and before we have made changes to the
> cache. In that case, we end up with a dirty page in cache when we
> shouldn't have any. This will be flushed later and will overwrite all
> subsequent writes to the part of the file represented by this page.
> 
> Before making any writes to the server, we need to confirm that we are
> not in the process of flushing data to the server and if we are, we
> should wait until the process is complete before we attempt the write.
> We should also wait for existing writes to complete before we process
> an oplock break request which changes oplock values.
> 
> We add a version specific  downgrade_oplock() operation to allow for
> differences in the oplock values set for the different smb versions.
> 
> Cc: stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Signed-off-by: Sachin Prabhu <sprabhu-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
>  fs/cifs/cifsfs.c    | 14 +++++++++-
>  fs/cifs/cifsglob.h  |  8 ++++++
>  fs/cifs/cifsproto.h |  3 +++
>  fs/cifs/file.c      | 31 +++++++++++++++++++---
>  fs/cifs/misc.c      | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++--
>  fs/cifs/smb1ops.c   | 11 ++++++++
>  fs/cifs/smb2misc.c  | 18 ++++++++++---
>  fs/cifs/smb2ops.c   | 14 ++++++++++
>  8 files changed, 164 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> index 849f613..7c6b73c 100644
> --- a/fs/cifs/cifsfs.c
> +++ b/fs/cifs/cifsfs.c
> @@ -253,6 +253,11 @@ cifs_alloc_inode(struct super_block *sb)
>  	cifs_set_oplock_level(cifs_inode, 0);
>  	cifs_inode->delete_pending = false;
>  	cifs_inode->invalid_mapping = false;
> +	clear_bit(CIFS_INODE_PENDING_OPLOCK_BREAK, &cifs_inode->flags);
> +	clear_bit(CIFS_INODE_PENDING_WRITERS, &cifs_inode->flags);
> +	clear_bit(CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2, &cifs_inode->flags);
> +	spin_lock_init(&cifs_inode->writers_lock);
> +	cifs_inode->writers = 0;
>  	cifs_inode->vfs_inode.i_blkbits = 14;  /* 2**14 = CIFS_MAX_MSGSIZE */
>  	cifs_inode->server_eof = 0;
>  	cifs_inode->uniqueid = 0;
> @@ -731,19 +736,26 @@ static ssize_t cifs_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
>  				   unsigned long nr_segs, loff_t pos)
>  {
>  	struct inode *inode = file_inode(iocb->ki_filp);
> +	struct cifsInodeInfo *cinode = CIFS_I(inode);
>  	ssize_t written;
>  	int rc;
>  
> +	written = cifs_get_writer(cinode);
> +	if (written)
> +		return written;
> +
>  	written = generic_file_aio_write(iocb, iov, nr_segs, pos);
>  
>  	if (CIFS_CACHE_WRITE(CIFS_I(inode)))
> -		return written;
> +		goto out;
>  
>  	rc = filemap_fdatawrite(inode->i_mapping);
>  	if (rc)
>  		cifs_dbg(FYI, "cifs_file_aio_write: %d rc on %p inode\n",
>  			 rc, inode);
>  
> +out:
> +	cifs_put_writer(cinode);
>  	return written;
>  }
>  
> diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> index cf32f03..8885ce8 100644
> --- a/fs/cifs/cifsglob.h
> +++ b/fs/cifs/cifsglob.h
> @@ -228,6 +228,8 @@ struct smb_version_operations {
>  	/* verify the message */
>  	int (*check_message)(char *, unsigned int);
>  	bool (*is_oplock_break)(char *, struct TCP_Server_Info *);
> +	void (*downgrade_oplock)(struct TCP_Server_Info *,
> +					struct cifsInodeInfo *, bool);
>  	/* process transaction2 response */
>  	bool (*check_trans2)(struct mid_q_entry *, struct TCP_Server_Info *,
>  			     char *, int);
> @@ -1113,6 +1115,12 @@ struct cifsInodeInfo {
>  	unsigned int epoch;		/* used to track lease state changes */
>  	bool delete_pending;		/* DELETE_ON_CLOSE is set */
>  	bool invalid_mapping;		/* pagecache is invalid */
> +	unsigned long flags;
> +#define CIFS_INODE_PENDING_OPLOCK_BREAK   (0) /* oplock break in progress */
> +#define CIFS_INODE_PENDING_WRITERS	  (1) /* Writes in progress */
> +#define CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2 (2) /* Downgrade oplock to L2 */
> +	spinlock_t writers_lock;
> +	unsigned int writers;		/* Number of writers on this inode */
>  	unsigned long time;		/* jiffies of last update of inode */
>  	u64  server_eof;		/* current file size on server -- protected by i_lock */
>  	u64  uniqueid;			/* server inode number */
> diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
> index acc4ee8..ca7980a 100644
> --- a/fs/cifs/cifsproto.h
> +++ b/fs/cifs/cifsproto.h
> @@ -127,6 +127,9 @@ extern u64 cifs_UnixTimeToNT(struct timespec);
>  extern struct timespec cnvrtDosUnixTm(__le16 le_date, __le16 le_time,
>  				      int offset);
>  extern void cifs_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock);
> +extern int cifs_get_writer(struct cifsInodeInfo *cinode);
> +extern void cifs_put_writer(struct cifsInodeInfo *cinode);
> +extern void cifs_done_oplock_break(struct cifsInodeInfo *cinode);
>  extern int cifs_unlock_range(struct cifsFileInfo *cfile,
>  			     struct file_lock *flock, const unsigned int xid);
>  extern int cifs_push_mandatory_locks(struct cifsFileInfo *cfile);
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 53c1507..9d07950 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -2620,12 +2620,20 @@ cifs_strict_writev(struct kiocb *iocb, const struct iovec *iov,
>  	struct cifs_tcon *tcon = tlink_tcon(cfile->tlink);
>  	ssize_t written;
>  
> +	written = cifs_get_writer(cinode);
> +	if (written)
> +		return written;
> +
>  	if (CIFS_CACHE_WRITE(cinode)) {
>  		if (cap_unix(tcon->ses) &&
>  		(CIFS_UNIX_FCNTL_CAP & le64_to_cpu(tcon->fsUnixInfo.Capability))
> -		    && ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NOPOSIXBRL) == 0))
> -			return generic_file_aio_write(iocb, iov, nr_segs, pos);
> -		return cifs_writev(iocb, iov, nr_segs, pos);
> +		  && ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NOPOSIXBRL) == 0)) {
> +			written = generic_file_aio_write(
> +					iocb, iov, nr_segs, pos);
> +			goto out;
> +		}
> +		written = cifs_writev(iocb, iov, nr_segs, pos);
> +		goto out;
>  	}
>  	/*
>  	 * For non-oplocked files in strict cache mode we need to write the data
> @@ -2645,6 +2653,8 @@ cifs_strict_writev(struct kiocb *iocb, const struct iovec *iov,
>  			 inode);
>  		cinode->oplock = 0;
>  	}
> +out:
> +	cifs_put_writer(cinode);
>  	return written;
>  }
>  
> @@ -3656,6 +3666,13 @@ static int cifs_launder_page(struct page *page)
>  	return rc;
>  }
>  
> +static int
> +cifs_pending_writers_wait(void *unused)
> +{
> +	schedule();
> +	return 0;
> +}
> +
>  void cifs_oplock_break(struct work_struct *work)
>  {
>  	struct cifsFileInfo *cfile = container_of(work, struct cifsFileInfo,
> @@ -3663,8 +3680,15 @@ void cifs_oplock_break(struct work_struct *work)
>  	struct inode *inode = cfile->dentry->d_inode;
>  	struct cifsInodeInfo *cinode = CIFS_I(inode);
>  	struct cifs_tcon *tcon = tlink_tcon(cfile->tlink);
> +	struct TCP_Server_Info *server = tcon->ses->server;
>  	int rc = 0;
>  
> +	wait_on_bit(&cinode->flags, CIFS_INODE_PENDING_WRITERS,
> +			cifs_pending_writers_wait, TASK_UNINTERRUPTIBLE);
> +
> +	server->ops->downgrade_oplock(server, cinode,
> +		test_bit(CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2, &cinode->flags));
> +
>  	if (!CIFS_CACHE_WRITE(cinode) && CIFS_CACHE_READ(cinode) &&
>  						cifs_has_mand_locks(cinode)) {
>  		cifs_dbg(FYI, "Reset oplock to None for inode=%p due to mand locks\n",
> @@ -3701,6 +3725,7 @@ void cifs_oplock_break(struct work_struct *work)
>  							     cinode);
>  		cifs_dbg(FYI, "Oplock release rc = %d\n", rc);
>  	}
> +	cifs_done_oplock_break(cinode);
>  }
>  
>  /*
> diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
> index 2f9f379..3b0c62e 100644
> --- a/fs/cifs/misc.c
> +++ b/fs/cifs/misc.c
> @@ -466,8 +466,22 @@ is_valid_oplock_break(char *buffer, struct TCP_Server_Info *srv)
>  				cifs_dbg(FYI, "file id match, oplock break\n");
>  				pCifsInode = CIFS_I(netfile->dentry->d_inode);
>  
> -				cifs_set_oplock_level(pCifsInode,
> -					pSMB->OplockLevel ? OPLOCK_READ : 0);
> +				set_bit(CIFS_INODE_PENDING_OPLOCK_BREAK,
> +					&pCifsInode->flags);
> +
> +				/*
> +				 * Set flag if the server downgrades the oplock
> +				 * to L2 else clear.
> +				 */
> +				if (pSMB->OplockLevel)
> +					set_bit(
> +					   CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2,
> +					   &pCifsInode->flags);
> +				else
> +					clear_bit(
> +					   CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2,
> +					   &pCifsInode->flags);
> +
>  				queue_work(cifsiod_wq,
>  					   &netfile->oplock_break);
>  				netfile->oplock_break_cancelled = false;
> @@ -551,6 +565,62 @@ void cifs_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock)
>  		cinode->oplock = 0;
>  }
>  
> +static int
> +cifs_oplock_break_wait(void *unused)
> +{
> +	schedule();
> +	return signal_pending(current) ? -ERESTARTSYS : 0;
> +}
> +
> +/*
> + * We wait for oplock breaks to be processed before we attempt to perform
> + * writes.
> + */
> +int cifs_get_writer(struct cifsInodeInfo *cinode)
> +{
> +	int rc;
> +
> +start:
> +	rc = wait_on_bit(&cinode->flags, CIFS_INODE_PENDING_OPLOCK_BREAK,
> +				   cifs_oplock_break_wait, TASK_KILLABLE);
> +	if (rc)
> +		return rc;
> +
> +	spin_lock(&cinode->writers_lock);
> +	if (!cinode->writers)
> +		set_bit(CIFS_INODE_PENDING_WRITERS, &cinode->flags);
> +	cinode->writers++;
> +	/* Check to see if we have started servicing an oplock break */
> +	if (test_bit(CIFS_INODE_PENDING_OPLOCK_BREAK, &cinode->flags)) {
> +		cinode->writers--;
> +		if (cinode->writers == 0) {
> +			clear_bit(CIFS_INODE_PENDING_WRITERS, &cinode->flags);
> +			wake_up_bit(&cinode->flags, CIFS_INODE_PENDING_WRITERS);
> +		}
> +		spin_unlock(&cinode->writers_lock);
> +		goto start;
> +	}
> +	spin_unlock(&cinode->writers_lock);
> +	return 0;
> +}
> +
> +void cifs_put_writer(struct cifsInodeInfo *cinode)
> +{
> +	spin_lock(&cinode->writers_lock);
> +	cinode->writers--;
> +	if (cinode->writers == 0) {
> +		clear_bit(CIFS_INODE_PENDING_WRITERS, &cinode->flags);
> +		wake_up_bit(&cinode->flags, CIFS_INODE_PENDING_WRITERS);
> +	}
> +	spin_unlock(&cinode->writers_lock);
> +}
> +
> +void cifs_done_oplock_break(struct cifsInodeInfo *cinode)
> +{
> +	clear_bit(CIFS_INODE_PENDING_OPLOCK_BREAK, &cinode->flags);
> +	wake_up_bit(&cinode->flags, CIFS_INODE_PENDING_OPLOCK_BREAK);
> +}
> +
>  bool
>  backup_cred(struct cifs_sb_info *cifs_sb)
>  {
> diff --git a/fs/cifs/smb1ops.c b/fs/cifs/smb1ops.c
> index 526fb89..2cc7d78 100644
> --- a/fs/cifs/smb1ops.c
> +++ b/fs/cifs/smb1ops.c
> @@ -372,6 +372,16 @@ coalesce_t2(char *second_buf, struct smb_hdr *target_hdr)
>  	return 0;
>  }
>  
> +void
> +cifs_downgrade_oplock(struct TCP_Server_Info *server,
> +			struct cifsInodeInfo *cinode, bool set_level2)
> +{
> +	if (set_level2)
> +		cifs_set_oplock_level(cinode, OPLOCK_READ);
> +	else
> +		cifs_set_oplock_level(cinode, 0);
> +}
> +
>  static bool
>  cifs_check_trans2(struct mid_q_entry *mid, struct TCP_Server_Info *server,
>  		  char *buf, int malformed)
> @@ -1019,6 +1029,7 @@ struct smb_version_operations smb1_operations = {
>  	.clear_stats = cifs_clear_stats,
>  	.print_stats = cifs_print_stats,
>  	.is_oplock_break = is_valid_oplock_break,
> +	.downgrade_oplock = cifs_downgrade_oplock,
>  	.check_trans2 = cifs_check_trans2,
>  	.need_neg = cifs_need_neg,
>  	.negotiate = cifs_negotiate,
> diff --git a/fs/cifs/smb2misc.c b/fs/cifs/smb2misc.c
> index fb39662..b8021fd 100644
> --- a/fs/cifs/smb2misc.c
> +++ b/fs/cifs/smb2misc.c
> @@ -575,9 +575,21 @@ smb2_is_valid_oplock_break(char *buffer, struct TCP_Server_Info *server)
>  				else
>  					cfile->oplock_break_cancelled = false;
>  
> -				server->ops->set_oplock_level(cinode,
> -				  rsp->OplockLevel ? SMB2_OPLOCK_LEVEL_II : 0,
> -				  0, NULL);
> +				set_bit(CIFS_INODE_PENDING_OPLOCK_BREAK,
> +					&cinode->flags);
> +
> +				/*
> +				 * Set flag if the server downgrades the oplock
> +				 * to L2 else clear.
> +				 */
> +				if (rsp->OplockLevel)
> +					set_bit(
> +					   CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2,
> +					   &cinode->flags);
> +				else
> +					clear_bit(
> +					   CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2,
> +					   &cinode->flags);
>  
>  				queue_work(cifsiod_wq, &cfile->oplock_break);
>  
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index 192f51a..ab8964d 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -904,6 +904,17 @@ smb2_query_symlink(const unsigned int xid, struct cifs_tcon *tcon,
>  	return rc;
>  }
>  
> +void
> +smb2_downgrade_oplock(struct TCP_Server_Info *server,
> +			struct cifsInodeInfo *cinode, bool set_level2)
> +{
> +	if (set_level2)
> +		server->ops->set_oplock_level(cinode, SMB2_OPLOCK_LEVEL_II,
> +						0, NULL);
> +	else
> +		server->ops->set_oplock_level(cinode, 0, 0, NULL);
> +}
> +
>  static void
>  smb2_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock,
>  		      unsigned int epoch, bool *purge_cache)
> @@ -1110,6 +1121,7 @@ struct smb_version_operations smb20_operations = {
>  	.clear_stats = smb2_clear_stats,
>  	.print_stats = smb2_print_stats,
>  	.is_oplock_break = smb2_is_valid_oplock_break,
> +	.downgrade_oplock = smb2_downgrade_oplock,
>  	.need_neg = smb2_need_neg,
>  	.negotiate = smb2_negotiate,
>  	.negotiate_wsize = smb2_negotiate_wsize,
> @@ -1184,6 +1196,7 @@ struct smb_version_operations smb21_operations = {
>  	.clear_stats = smb2_clear_stats,
>  	.print_stats = smb2_print_stats,
>  	.is_oplock_break = smb2_is_valid_oplock_break,
> +	.downgrade_oplock = smb2_downgrade_oplock,
>  	.need_neg = smb2_need_neg,
>  	.negotiate = smb2_negotiate,
>  	.negotiate_wsize = smb2_negotiate_wsize,
> @@ -1259,6 +1272,7 @@ struct smb_version_operations smb30_operations = {
>  	.print_stats = smb2_print_stats,
>  	.dump_share_caps = smb2_dump_share_caps,
>  	.is_oplock_break = smb2_is_valid_oplock_break,
> +	.downgrade_oplock = smb2_downgrade_oplock,
>  	.need_neg = smb2_need_neg,
>  	.negotiate = smb2_negotiate,
>  	.negotiate_wsize = smb2_negotiate_wsize,

Looks good.

I still think we need to fix the set_oplock_level operation, but this is fine
for an interim fix.

Reviewed-by: Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>