linux-kernel - [tip: locking/urgent] locking/lockdep: Remove more raw_cpu

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Date:   Sat, 31 Oct 2020 11:30:32 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: locking/urgent] locking/lockdep: Remove more raw_cpu_read() usage

The following commit has been merged into the locking/urgent branch of tip:

Commit-ID:     d48e3850030623e1c20785bceaaf78f916d0b1a3
Gitweb:        https://git.kernel.org/tip/d48e3850030623e1c20785bceaaf78f916d0b1a3
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Mon, 26 Oct 2020 16:22:56 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 30 Oct 2020 17:07:18 +01:00

locking/lockdep: Remove more raw_cpu_read() usage

I initially thought raw_cpu_read() was OK, since if it is !0 we have
IRQs disabled and can't get migrated, so if we get migrated both CPUs
must have 0 and it doesn't matter which 0 we read.

And while that is true; it isn't the whole store, on pretty much all
architectures (except x86) this can result in computing the address for
one CPU, getting migrated, the old CPU continuing execution with another
task (possibly setting recursion) and then the new CPU reading the value
of the old CPU, which is no longer 0.

Similer to:

  baffd723e44d ("lockdep: Revert "lockdep: Use raw_cpu_*() for per-cpu variables"")

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20201026152256.GB2651@hirez.programming.kicks-ass.net
---
 kernel/locking/lockdep.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index fc206ae..1102849 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -84,7 +84,7 @@ static inline bool lockdep_enabled(void)
 	if (!debug_locks)
 		return false;
 
-	if (raw_cpu_read(lockdep_recursion))
+	if (this_cpu_read(lockdep_recursion))
 		return false;
 
 	if (current->lockdep_recursion)