vfs: fix RCU-lockdep false positive due to /proc
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@gmail.com> Located-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Al Viro <viro@ZenIV.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -61,7 +61,8 @@ struct files_struct {
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(rcu_dereference_check((fdtfd), \
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rcu_read_lock_held() || \
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lockdep_is_held(&(files)->file_lock) || \
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atomic_read(&(files)->count) == 1))
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atomic_read(&(files)->count) == 1 || \
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rcu_my_thread_group_empty()))
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#define files_fdtable(files) \
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(rcu_dereference_check_fdtable((files), (files)->fdt))
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