On Fri, 2025-12-05 at 16:18 +0900, Byungchul Park wrote: > 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 <[email protected]> > Signed-off-by: Byungchul Park <[email protected]> > --- > 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 */
Seems fine to me. Reviewed-by: Jeff Layton <[email protected]>
