The patch titled
vfs: fix RCU-lockdep false positive due to /proc
has been added to the -mm tree. Its filename is
vfs-fix-rcu-lockdep-false-positive-due-to-proc.patch
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------------------------------------------------------
Subject: vfs: fix RCU-lockdep false positive due to /proc
From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
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 uses the wrapper for
thread_group_empty(current) defined by rcu_my_thread_group_empty()
provided in a separate commit.
Located-by: Miles Lane <miles.lane@xxxxxxxxx>
Located-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/fdtable.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff -puN include/linux/fdtable.h~vfs-fix-rcu-lockdep-false-positive-due-to-proc include/linux/fdtable.h
--- a/include/linux/fdtable.h~vfs-fix-rcu-lockdep-false-positive-due-to-proc
+++ a/include/linux/fdtable.h
@@ -62,7 +62,8 @@ 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))
_
Patches currently in -mm which might be from paulmck@xxxxxxxxxxxxxxxxxx are
origin.patch
fs-fcntlc-kill_fasync_rcu-fa_lock-must-be-irq-safe.patch
linux-next.patch
vfs-fix-rcu-lockdep-false-positive-due-to-proc.patch
vfs-use-kmalloc-to-allocate-fdmem-if-possible.patch
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