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| author | peterz@infradead.org <peterz@infradead.org> | 2020-09-02 18:03:23 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2020-09-03 11:19:42 +0200 |
| commit | 23870f1227680d2aacff6f79c3ab2222bd04e86e (patch) | |
| tree | 46cfafbbcc57f372200072c6784d91145c6b6984 /kernel/locking/lockdep_internals.h | |
| parent | fc3abb53250a90ba2150eebd182137c136f4d25a (diff) | |
| download | lwn-23870f1227680d2aacff6f79c3ab2222bd04e86e.tar.gz lwn-23870f1227680d2aacff6f79c3ab2222bd04e86e.zip | |
locking/lockdep: Fix "USED" <- "IN-NMI" inversions
During the LPC RCU BoF Paul asked how come the "USED" <- "IN-NMI"
detector doesn't trip over rcu_read_lock()'s lockdep annotation.
Looking into this I found a very embarrasing typo in
verify_lock_unused():
- if (!(class->usage_mask & LOCK_USED))
+ if (!(class->usage_mask & LOCKF_USED))
fixing that will indeed cause rcu_read_lock() to insta-splat :/
The above typo means that instead of testing for: 0x100 (1 <<
LOCK_USED), we test for 8 (LOCK_USED), which corresponds to (1 <<
LOCK_ENABLED_HARDIRQ).
So instead of testing for _any_ used lock, it will only match any lock
used with interrupts enabled.
The rcu_read_lock() annotation uses .check=0, which means it will not
set any of the interrupt bits and will thus never match.
In order to properly fix the situation and allow rcu_read_lock() to
correctly work, split LOCK_USED into LOCK_USED and LOCK_USED_READ and by
having .read users set USED_READ and test USED, pure read-recursive
locks are permitted.
Fixes: f6f48e180404 ("lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20200902160323.GK1362448@hirez.programming.kicks-ass.net
Diffstat (limited to 'kernel/locking/lockdep_internals.h')
| -rw-r--r-- | kernel/locking/lockdep_internals.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h index baca699b94e9..b0be1560ed17 100644 --- a/kernel/locking/lockdep_internals.h +++ b/kernel/locking/lockdep_internals.h @@ -19,6 +19,7 @@ enum lock_usage_bit { #include "lockdep_states.h" #undef LOCKDEP_STATE LOCK_USED, + LOCK_USED_READ, LOCK_USAGE_STATES }; @@ -40,6 +41,7 @@ enum { #include "lockdep_states.h" #undef LOCKDEP_STATE __LOCKF(USED) + __LOCKF(USED_READ) }; #define LOCKDEP_STATE(__STATE) LOCKF_ENABLED_##__STATE | |