Messages in this thread Patch in this message | | | Date | Tue, 14 Jan 2020 13:49:19 +0100 | Subject | [PATCH -rcu] kcsan: Make KCSAN compatible with lockdep | From | Marco Elver <> |
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To avoid unexpected reentry into lockdep's IRQ tracing code via KCSAN (if TRACE_IRQFLAGS is enabled), (1) use raw versions of local_irq_{save,restore} in kcsan_setup_watchpoint(), and (2) disable lockdep in kcsan_report() to avoid IRQ flags tracing upon generating the report.
Tested with:
CONFIG_LOCKDEP=y CONFIG_DEBUG_LOCKDEP=y
Where previously, the following warning (and variants with different stack traces) was consistently generated, with the fix introduced in this patch, the warning cannot be reproduced.
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> --- kernel/kcsan/core.c | 4 ++-- kernel/kcsan/report.c | 11 +++++++++++ kernel/locking/Makefile | 3 +++ 3 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index 87bf857c8893..e75f3dbf627e 100644 --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -337,7 +337,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) * detection point of view) to simply disable preemptions to ensure * as many tasks as possible run on other CPUs. */ - local_irq_save(irq_flags); + raw_local_irq_save(irq_flags); watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write); if (watchpoint == NULL) { @@ -429,7 +429,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 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); } diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c index b5b4feea49de..57ab7ef9786c 100644 --- a/kernel/kcsan/report.c +++ b/kernel/kcsan/report.c @@ -2,6 +2,7 @@ #include <linux/jiffies.h> #include <linux/kernel.h> +#include <linux/lockdep.h> #include <linux/preempt.h> #include <linux/printk.h> #include <linux/sched.h> @@ -410,6 +411,14 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type, { unsigned long flags = 0; + /* + * With TRACE_IRQFLAGS, lockdep's internal IRQ flags state becomes + * corrupted if we do not turn off lockdep. The likely cause is + * unexpected reentry into IRQ tracing code via KCSAN if we detect a + * data race. + */ + 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) @@ -418,4 +427,6 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type, release_report(&flags, type); } kcsan_enable_current(); + + lockdep_on(); } diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile index 45452facff3b..6d11cfb9b41f 100644 --- a/kernel/locking/Makefile +++ b/kernel/locking/Makefile @@ -5,6 +5,9 @@ KCOV_INSTRUMENT := n 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) -- 2.25.0.rc1.283.g88dfdc4193-goog
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