The following commit has been merged into the core/rcu branch of tip: Commit-ID: 90c018942c2babab73814648b37808fc3bf2ed1a Gitweb: https://git.kernel.org/tip/90c018942c2babab73814648b37808fc3bf2ed1a Author: Eric Dumazet <edumazet@xxxxxxxxxx> AuthorDate: Thu, 07 Nov 2019 11:37:38 -08:00 Committer: Paul E. McKenney <paulmck@xxxxxxxxxx> CommitterDate: Thu, 20 Feb 2020 15:58:22 -08:00 timer: Use hlist_unhashed_lockless() in timer_pending() The timer_pending() function is mostly used in lockless contexts, so Without proper annotations, KCSAN might detect a data-race [1]. Using hlist_unhashed_lockless() instead of hand-coding it seems appropriate (as suggested by Paul E. McKenney). [1] BUG: KCSAN: data-race in del_timer / detach_if_pending write to 0xffff88808697d870 of 8 bytes by task 10 on cpu 0: __hlist_del include/linux/list.h:764 [inline] detach_timer kernel/time/timer.c:815 [inline] detach_if_pending+0xcd/0x2d0 kernel/time/timer.c:832 try_to_del_timer_sync+0x60/0xb0 kernel/time/timer.c:1226 del_timer_sync+0x6b/0xa0 kernel/time/timer.c:1365 schedule_timeout+0x2d2/0x6e0 kernel/time/timer.c:1896 rcu_gp_fqs_loop+0x37c/0x580 kernel/rcu/tree.c:1639 rcu_gp_kthread+0x143/0x230 kernel/rcu/tree.c:1799 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352 read to 0xffff88808697d870 of 8 bytes by task 12060 on cpu 1: del_timer+0x3b/0xb0 kernel/time/timer.c:1198 sk_stop_timer+0x25/0x60 net/core/sock.c:2845 inet_csk_clear_xmit_timers+0x69/0xa0 net/ipv4/inet_connection_sock.c:523 tcp_clear_xmit_timers include/net/tcp.h:606 [inline] tcp_v4_destroy_sock+0xa3/0x3f0 net/ipv4/tcp_ipv4.c:2096 inet_csk_destroy_sock+0xf4/0x250 net/ipv4/inet_connection_sock.c:836 tcp_close+0x6f3/0x970 net/ipv4/tcp.c:2497 inet_release+0x86/0x100 net/ipv4/af_inet.c:427 __sock_release+0x85/0x160 net/socket.c:590 sock_close+0x24/0x30 net/socket.c:1268 __fput+0x1e1/0x520 fs/file_table.c:280 ____fput+0x1f/0x30 fs/file_table.c:313 task_work_run+0xf6/0x130 kernel/task_work.c:113 tracehook_notify_resume include/linux/tracehook.h:188 [inline] exit_to_usermode_loop+0x2b4/0x2c0 arch/x86/entry/common.c:163 Reported by Kernel Concurrency Sanitizer on: CPU: 1 PID: 12060 Comm: syz-executor.5 Not tainted 5.4.0-rc3+ #0 Hardware name: Google Google Compute Engine/Google Compute Engine, Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> [ paulmck: Pulled in Eric's later amendments. ] Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- include/linux/timer.h | 2 +- kernel/time/timer.c | 7 ++++--- 2 files changed, 5 insertions(+), 4 deletions(-) diff --git a/include/linux/timer.h b/include/linux/timer.h index 1e6650e..0dc19a8 100644 --- a/include/linux/timer.h +++ b/include/linux/timer.h @@ -164,7 +164,7 @@ static inline void destroy_timer_on_stack(struct timer_list *timer) { } */ static inline int timer_pending(const struct timer_list * timer) { - return timer->entry.pprev != NULL; + return !hlist_unhashed_lockless(&timer->entry); } extern void add_timer_on(struct timer_list *timer, int cpu); diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 4820823..568564a 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -944,6 +944,7 @@ static struct timer_base *lock_timer_base(struct timer_list *timer, #define MOD_TIMER_PENDING_ONLY 0x01 #define MOD_TIMER_REDUCE 0x02 +#define MOD_TIMER_NOTPENDING 0x04 static inline int __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int options) @@ -960,7 +961,7 @@ __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int option * the timer is re-modified to have the same timeout or ends up in the * same array bucket then just return: */ - if (timer_pending(timer)) { + if (!(options & MOD_TIMER_NOTPENDING) && timer_pending(timer)) { /* * The downside of this optimization is that it can result in * larger granularity than you would get from adding a new @@ -1133,7 +1134,7 @@ EXPORT_SYMBOL(timer_reduce); void add_timer(struct timer_list *timer) { BUG_ON(timer_pending(timer)); - mod_timer(timer, timer->expires); + __mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING); } EXPORT_SYMBOL(add_timer); @@ -1891,7 +1892,7 @@ signed long __sched schedule_timeout(signed long timeout) timer.task = current; timer_setup_on_stack(&timer.timer, process_timeout, 0); - __mod_timer(&timer.timer, expire, 0); + __mod_timer(&timer.timer, expire, MOD_TIMER_NOTPENDING); schedule(); del_singleshot_timer_sync(&timer.timer);
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