While compiling Linux kernel with DEPT on, the following error was observed:
./include/linux/rcupdate.h:1084:17: note: in expansion of macro ‘BUILD_BUG_ON’ 1084 | BUILD_BUG_ON(offsetof(typeof(*(ptr)), rhf) >= 4096); \ | ^~~~~~~~~~~~ ./include/linux/rcupdate.h:1047:29: note: in expansion of macro 'kvfree_rcu_arg_2' 1047 | #define kfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf) | ^~~~~~~~~~~~~~~~ net/sunrpc/xprt.c:1856:9: note: in expansion of macro 'kfree_rcu' 1856 | kfree_rcu(xprt, rcu); | ^~~~~~~~~ CC net/kcm/kcmproc.o make[4]: *** [scripts/Makefile.build:203: net/sunrpc/xprt.o] Error 1
Since kfree_rcu() assumes 'offset of struct rcu_head in a rcu-managed struct < 4096', the offest of struct rcu_head in struct rpc_xprt should not exceed 4096 but does, due to the debug information added by DEPT.
Relocate struct rcu_head to the first field of struct rpc_xprt from an arbitrary location to avoid the issue and meet the assumption.
Reported-by: Yunseong Kim ysk@kzalloc.com Signed-off-by: Byungchul Park byungchul@sk.com --- include/linux/sunrpc/xprt.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h index f46d1fb8f71a..666e42a17a31 100644 --- a/include/linux/sunrpc/xprt.h +++ b/include/linux/sunrpc/xprt.h @@ -211,6 +211,14 @@ enum xprt_transports {
struct rpc_sysfs_xprt; struct rpc_xprt { + /* + * Place struct rcu_head within the first 4096 bytes of struct + * rpc_xprt if sizeof(struct rpc_xprt) > 4096, so that + * kfree_rcu() can simply work assuming that. See the comment + * in kfree_rcu(). + */ + struct rcu_head rcu; + struct kref kref; /* Reference count */ const struct rpc_xprt_ops *ops; /* transport methods */ unsigned int id; /* transport id */ @@ -317,7 +325,6 @@ struct rpc_xprt { #if IS_ENABLED(CONFIG_SUNRPC_DEBUG) struct dentry *debugfs; /* debugfs directory */ #endif - struct rcu_head rcu; const struct xprt_class *xprt_class; struct rpc_sysfs_xprt *xprt_sysfs; bool main; /*mark if this is the 1st transport */