We must avoid any recursion into lockdep if KCSAN is enabled on utilities
used by lockdep. One manifestation of this is corruption of lockdep's
IRQ trace state (if TRACE_IRQFLAGS), resulting in spurious warnings
(see below). This commit fixes this by:
1. Using raw_local_irq{save,restore} in kcsan_setup_watchpoint().
2. Disabling lockdep in kcsan_report().
Tested with:
CONFIG_LOCKDEP=y
CONFIG_DEBUG_LOCKDEP=y
CONFIG_TRACE_IRQFLAGS=y
This fix eliminates spurious warnings such as the following one:
WARNING: CPU: 0 PID: 2 at kernel/locking/lockdep.c:4406 check_flags.part.0+0x101/0x220
Modules linked in:
CPU: 0 PID: 2 Comm: kthreadd Not tainted 5.5.0-rc1+ #11
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
RIP: 0010:check_flags.part.0+0x101/0x220
<snip>
Call Trace:
lock_is_held_type+0x69/0x150
freezer_fork+0x20b/0x370
cgroup_post_fork+0x2c9/0x5c0
copy_process+0x2675/0x3b40
_do_fork+0xbe/0xa30
? _raw_spin_unlock_irqrestore+0x40/0x50
? match_held_lock+0x56/0x250
? kthread_park+0xf0/0xf0
kernel_thread+0xa6/0xd0
? kthread_park+0xf0/0xf0
kthreadd+0x321/0x3d0
? kthread_create_on_cpu+0x130/0x130
ret_from_fork+0x3a/0x50
irq event stamp: 64
hardirqs last enabled at (63): [<
ffffffff9a7995d0>] _raw_spin_unlock_irqrestore+0x40/0x50
hardirqs last disabled at (64): [<
ffffffff992a96d2>] kcsan_setup_watchpoint+0x92/0x460
softirqs last enabled at (32): [<
ffffffff990489b8>] fpu__copy+0xe8/0x470
softirqs last disabled at (30): [<
ffffffff99048939>] fpu__copy+0x69/0x470
Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Marco Elver <elver@google.com>
Acked-by: Alexander Potapenko <glider@google.com>
Tested-by: Qian Cai <cai@lca.pw>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
* CPU-local data accesses), it makes more sense (from a data race
* detection point of view) to simply disable preemptions to ensure
* as many tasks as possible run on other CPUs.
+ *
+ * Use raw versions, to avoid lockdep recursion via IRQ flags tracing.
*/
- local_irq_save(irq_flags);
+ raw_local_irq_save(irq_flags);
watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
if (watchpoint == NULL) {
kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS);
out_unlock:
- local_irq_restore(irq_flags);
+ raw_local_irq_restore(irq_flags);
out:
user_access_restore(ua_flags);
}
#include <linux/jiffies.h>
#include <linux/kernel.h>
+#include <linux/lockdep.h>
#include <linux/preempt.h>
#include <linux/printk.h>
#include <linux/sched.h>
{
unsigned long flags = 0;
+ /*
+ * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if
+ * we do not turn off lockdep here; this could happen due to recursion
+ * into lockdep via KCSAN if we detect a data race in utilities used by
+ * lockdep.
+ */
+ lockdep_off();
+
kcsan_disable_current();
if (prepare_report(&flags, ptr, size, access_type, cpu_id, type)) {
if (print_report(ptr, size, access_type, value_change, cpu_id, type) && panic_on_warn)
release_report(&flags, type);
}
kcsan_enable_current();
+
+ lockdep_on();
}
obj-y += mutex.o semaphore.o rwsem.o percpu-rwsem.o
+# Avoid recursion lockdep -> KCSAN -> ... -> lockdep.
+KCSAN_SANITIZE_lockdep.o := n
+
ifdef CONFIG_FUNCTION_TRACER
CFLAGS_REMOVE_lockdep.o = $(CC_FLAGS_FTRACE)
CFLAGS_REMOVE_lockdep_proc.o = $(CC_FLAGS_FTRACE)