[PATCH tip/core/urgent 10/10] vfs: fix RCU-lockdep false positive due to /proc access
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From: Paul E. McKenney on 3 May 2010 15:00 If a single-threaded process does a file-descriptor operation, and some other process accesses that same file descriptor via /proc, the current rcu_dereference_check_fdtable() can give a false-positive RCU-lockdep splat due to the reference count being increased by the /proc access after the reference-count check in fget_light() but before the check in rcu_dereference_check_fdtable(). This commit prevents this false positive by checking for a single-threaded process. To avoid #include hell, this commit also introduces an rcu_my_thread_group_empty() as a wrapper for thread_group_empty(current). Located-by: Miles Lane <miles.lane(a)gmail.com> Located-by: Eric Dumazet <eric.dumazet(a)gmail.com> Signed-off-by: Paul E. McKenney <paulmck(a)linux.vnet.ibm.com> Cc: Al Viro <viro(a)ZenIV.linux.org.uk> --- include/linux/fdtable.h | 3 ++- include/linux/rcupdate.h | 2 ++ kernel/rcupdate.c | 11 +++++++++++ 3 files changed, 15 insertions(+), 1 deletions(-) diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h index 013dc52..d147461 100644 --- a/include/linux/fdtable.h +++ b/include/linux/fdtable.h @@ -61,7 +61,8 @@ struct files_struct { (rcu_dereference_check((fdtfd), \ rcu_read_lock_held() || \ lockdep_is_held(&(files)->file_lock) || \ - atomic_read(&(files)->count) == 1)) + atomic_read(&(files)->count) == 1 || \ + rcu_my_thread_group_empty())) #define files_fdtable(files) \ (rcu_dereference_check_fdtable((files), (files)->fdt)) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index ec9ab49..4dca275 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -190,6 +190,8 @@ static inline int rcu_read_lock_sched_held(void) #ifdef CONFIG_PROVE_RCU +extern int rcu_my_thread_group_empty(void); + #define __do_rcu_dereference_check(c) \ do { \ static bool __warned; \ diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 03a7ea1..49d808e 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -122,3 +122,14 @@ void wakeme_after_rcu(struct rcu_head *head) rcu = container_of(head, struct rcu_synchronize, head); complete(&rcu->completion); } + +#ifdef CONFIG_PROVE_RCU +/* + * wrapper function to avoid #include problems. + */ +int rcu_my_thread_group_empty(void) +{ + return thread_group_empty(current); +} +EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty); +#endif /* #ifdef CONFIG_PROVE_RCU */ -- 1.7.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |