afs: Fix speculative status fetches

[ Upstream commit 22650f148126571be1098d34160eb4931fc77241 ]

The generic/464 xfstest causes kAFS to emit occasional warnings of the
form:

        kAFS: vnode modified {100055:8a} 30->31 YFS.StoreData64 (c=6015)

This indicates that the data version received back from the server did not
match the expected value (the DV should be incremented monotonically for
each individual modification op committed to a vnode).

What is happening is that a lookup call is doing a bulk status fetch
speculatively on a bunch of vnodes in a directory besides getting the
status of the vnode it's actually interested in.  This is racing with a
StoreData operation (though it could also occur with, say, a MakeDir op).

On the client, a modification operation locks the vnode, but the bulk
status fetch only locks the parent directory, so no ordering is imposed
there (thereby avoiding an avenue to deadlock).

On the server, the StoreData op handler doesn't lock the vnode until it's
received all the request data, and downgrades the lock after committing the
data until it has finished sending change notifications to other clients -
which allows the status fetch to occur before it has finished.

This means that:

 - a status fetch can access the target vnode either side of the exclusive
   section of the modification

 - the status fetch could start before the modification, yet finish after,
   and vice-versa.

 - the status fetch and the modification RPCs can complete in either order.

 - the status fetch can return either the before or the after DV from the
   modification.

 - the status fetch might regress the locally cached DV.

Some of these are handled by the previous fix[1], but that's not sufficient
because it checks the DV it received against the DV it cached at the start
of the op, but the DV might've been updated in the meantime by a locally
generated modification op.

Fix this by the following means:

 (1) Keep track of when we're performing a modification operation on a
     vnode.  This is done by marking vnode parameters with a 'modification'
     note that causes the AFS_VNODE_MODIFYING flag to be set on the vnode
     for the duration.

 (2) Alter the speculation race detection to ignore speculative status
     fetches if either the vnode is marked as being modified or the data
     version number is not what we expected.

Note that whilst the "vnode modified" warning does get recovered from as it
causes the client to refetch the status at the next opportunity, it will
also invalidate the pagecache, so changes might get lost.

Fixes: a9e5c87ca744 ("afs: Fix speculative status fetch going out of order wrt to modifications")
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-and-reviewed-by: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/160605082531.252452.14708077925602709042.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/linux-fsdevel/161961335926.39335.2552653972195467566.stgit@warthog.procyon.org.uk/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 17548c1faf02999c7c631dd559fcaf2c430af607..31251d11d576c3cab978ae1ecc50401d11f7087f 100644 (file)
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -1342,6 +1342,7 @@ static int afs_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
 
        afs_op_set_vnode(op, 0, dvnode);
        op->file[0].dv_delta = 1;
+       op->file[0].modification = true;
        op->file[0].update_ctime = true;
        op->dentry      = dentry;
        op->create.mode = S_IFDIR | mode;
@@ -1423,6 +1424,7 @@ static int afs_rmdir(struct inode *dir, struct dentry *dentry)
 
        afs_op_set_vnode(op, 0, dvnode);
        op->file[0].dv_delta = 1;
+       op->file[0].modification = true;
        op->file[0].update_ctime = true;
 
        op->dentry      = dentry;
@@ -1559,6 +1561,7 @@ static int afs_unlink(struct inode *dir, struct dentry *dentry)
 
        afs_op_set_vnode(op, 0, dvnode);
        op->file[0].dv_delta = 1;
+       op->file[0].modification = true;
        op->file[0].update_ctime = true;
 
        /* Try to make sure we have a callback promise on the victim. */
@@ -1641,6 +1644,7 @@ static int afs_create(struct user_namespace *mnt_userns, struct inode *dir,
 
        afs_op_set_vnode(op, 0, dvnode);
        op->file[0].dv_delta = 1;
+       op->file[0].modification = true;
        op->file[0].update_ctime = true;
 
        op->dentry      = dentry;
@@ -1715,6 +1719,7 @@ static int afs_link(struct dentry *from, struct inode *dir,
        afs_op_set_vnode(op, 0, dvnode);
        afs_op_set_vnode(op, 1, vnode);
        op->file[0].dv_delta = 1;
+       op->file[0].modification = true;
        op->file[0].update_ctime = true;
        op->file[1].update_ctime = true;
 
@@ -1910,6 +1915,8 @@ static int afs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
        afs_op_set_vnode(op, 1, new_dvnode); /* May be same as orig_dvnode */
        op->file[0].dv_delta = 1;
        op->file[1].dv_delta = 1;
+       op->file[0].modification = true;
+       op->file[1].modification = true;
        op->file[0].update_ctime = true;
        op->file[1].update_ctime = true;
 

diff --git a/fs/afs/dir_silly.c b/fs/afs/dir_silly.c
index 04f75a44f2432dc1bcbfb473275c605bcb7ee945..dae9a57d7ec0c11b105ffa7fc26c3da40d9a7158 100644 (file)
--- a/fs/afs/dir_silly.c
+++ b/fs/afs/dir_silly.c
@@ -73,6 +73,8 @@ static int afs_do_silly_rename(struct afs_vnode *dvnode, struct afs_vnode *vnode
        afs_op_set_vnode(op, 1, dvnode);
        op->file[0].dv_delta = 1;
        op->file[1].dv_delta = 1;
+       op->file[0].modification = true;
+       op->file[1].modification = true;
        op->file[0].update_ctime = true;
        op->file[1].update_ctime = true;
 
@@ -201,6 +203,7 @@ static int afs_do_silly_unlink(struct afs_vnode *dvnode, struct afs_vnode *vnode
        afs_op_set_vnode(op, 0, dvnode);
        afs_op_set_vnode(op, 1, vnode);
        op->file[0].dv_delta = 1;
+       op->file[0].modification = true;
        op->file[0].update_ctime = true;
        op->file[1].op_unlinked = true;
        op->file[1].update_ctime = true;

diff --git a/fs/afs/fs_operation.c b/fs/afs/fs_operation.c
index 71c58723763d23bf116353c405b5fcd78c8039cd..a82515b47350e66fcffec8c39da9a68df67d0e0c 100644 (file)
--- a/fs/afs/fs_operation.c
+++ b/fs/afs/fs_operation.c
@@ -118,6 +118,8 @@ static void afs_prepare_vnode(struct afs_operation *op, struct afs_vnode_param *
                vp->cb_break_before     = afs_calc_vnode_cb_break(vnode);
                if (vnode->lock_state != AFS_VNODE_LOCK_NONE)
                        op->flags       |= AFS_OPERATION_CUR_ONLY;
+               if (vp->modification)
+                       set_bit(AFS_VNODE_MODIFYING, &vnode->flags);
        }
 
        if (vp->fid.vnode)
@@ -223,6 +225,10 @@ int afs_put_operation(struct afs_operation *op)
 
        if (op->ops && op->ops->put)
                op->ops->put(op);
+       if (op->file[0].modification)
+               clear_bit(AFS_VNODE_MODIFYING, &op->file[0].vnode->flags);
+       if (op->file[1].modification && op->file[1].vnode != op->file[0].vnode)
+               clear_bit(AFS_VNODE_MODIFYING, &op->file[1].vnode->flags);
        if (op->file[0].put_vnode)
                iput(&op->file[0].vnode->vfs_inode);
        if (op->file[1].put_vnode)

diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index 5a70c09f532523dc4ca394eeaa0f69a82ed13119..fddf7d54e0b76b87cd4e4884aaa874ecb34c5311 100644 (file)
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -293,8 +293,9 @@ void afs_vnode_commit_status(struct afs_operation *op, struct afs_vnode_param *v
                        op->flags &= ~AFS_OPERATION_DIR_CONFLICT;
                }
        } else if (vp->scb.have_status) {
-               if (vp->dv_before + vp->dv_delta != vp->scb.status.data_version &&
-                   vp->speculative)
+               if (vp->speculative &&
+                   (test_bit(AFS_VNODE_MODIFYING, &vnode->flags) ||
+                    vp->dv_before != vnode->status.data_version))
                        /* Ignore the result of a speculative bulk status fetch
                         * if it splits around a modification op, thereby
                         * appearing to regress the data version.
@@ -910,6 +911,7 @@ int afs_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
        }
        op->ctime = attr->ia_ctime;
        op->file[0].update_ctime = 1;
+       op->file[0].modification = true;
 
        op->ops = &afs_setattr_operation;
        ret = afs_do_sync_operation(op);

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 1627b1872812570da753f85c5fad8059245ad984..be981a9a1add2bf414c00415d107a8ec8019b3b9 100644 (file)
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -640,6 +640,7 @@ struct afs_vnode {
 #define AFS_VNODE_PSEUDODIR    7               /* set if Vnode is a pseudo directory */
 #define AFS_VNODE_NEW_CONTENT  8               /* Set if file has new content (create/trunc-0) */
 #define AFS_VNODE_SILLY_DELETED        9               /* Set if file has been silly-deleted */
+#define AFS_VNODE_MODIFYING    10              /* Set if we're performing a modification op */
 
        struct list_head        wb_keys;        /* List of keys available for writeback */
        struct list_head        pending_locks;  /* locks waiting to be granted */
@@ -756,6 +757,7 @@ struct afs_vnode_param {
        bool                    set_size:1;     /* Must update i_size */
        bool                    op_unlinked:1;  /* True if file was unlinked by op */
        bool                    speculative:1;  /* T if speculative status fetch (no vnode lock) */
+       bool                    modification:1; /* Set if the content gets modified */
 };
 
 /*

diff --git a/fs/afs/write.c b/fs/afs/write.c
index eb737ed63afb6041f26207171b95960e5ec6e7a9..ebe3b6493fcef1b170cba6a451de55906b962ba0 100644 (file)
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -450,6 +450,7 @@ static int afs_store_data(struct address_space *mapping,
        afs_op_set_vnode(op, 0, vnode);
        op->file[0].dv_delta = 1;
        op->store.mapping = mapping;
+       op->file[0].modification = true;
        op->store.first = first;
        op->store.last = last;
        op->store.first_offset = offset;