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Subject[PATCH 7/8] afs: Mark afs_net::ws_cell as __rcu and set using rcu functions
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The afs_net::ws_cell member is sometimes used under RCU conditions from
within an seq-readlock. It isn't, however, marked __rcu and it isn't set
using the proper RCU barrier-imposing functions.

Fix this by annotating it with __rcu and using appropriate barriers to
make sure accesses are correctly ordered.

Without this, the code can produce the following warning:

>> fs/afs/proc.c:151:24: sparse: incompatible types in comparison expression (different address spaces)

Fixes: f044c8847bb6 ("afs: Lay the groundwork for supporting network namespaces")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: David Howells <dhowells@redhat.com>
---

fs/afs/cell.c | 8 ++++----
fs/afs/internal.h | 2 +-
fs/afs/proc.c | 2 +-
3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index fdf4c36cff79..80fd127239ce 100644
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -341,8 +341,8 @@ int afs_cell_init(struct afs_net *net, const char *rootcell)

/* install the new cell */
write_seqlock(&net->cells_lock);
- old_root = net->ws_cell;
- net->ws_cell = new_root;
+ old_root = rcu_access_pointer(net->ws_cell);
+ rcu_assign_pointer(net->ws_cell, new_root);
write_sequnlock(&net->cells_lock);

afs_put_cell(net, old_root);
@@ -755,8 +755,8 @@ void afs_cell_purge(struct afs_net *net)
_enter("");

write_seqlock(&net->cells_lock);
- ws = net->ws_cell;
- net->ws_cell = NULL;
+ ws = rcu_access_pointer(net->ws_cell);
+ RCU_INIT_POINTER(net->ws_cell, NULL);
write_sequnlock(&net->cells_lock);
afs_put_cell(net, ws);

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index f8086ec95e24..5d922ad148a8 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -231,7 +231,7 @@ struct afs_net {

/* Cell database */
struct rb_root cells;
- struct afs_cell *ws_cell;
+ struct afs_cell __rcu *ws_cell;
struct work_struct cells_manager;
struct timer_list cells_timer;
atomic_t cells_outstanding;
diff --git a/fs/afs/proc.c b/fs/afs/proc.c
index b45ee7576aa8..362f281b1b16 100644
--- a/fs/afs/proc.c
+++ b/fs/afs/proc.c
@@ -173,7 +173,7 @@ static ssize_t afs_proc_rootcell_read(struct file *file, char __user *buf,

if (*_pos > 0)
return 0;
- if (!net->ws_cell)
+ if (!rcu_access_pointer(net->ws_cell))
return 0;

rcu_read_lock();
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