On 2016/1/21 15:29, Ingo Molnar wrote: > > Cc:-ed other gents who touched the mutex code recently. Mail quoted below. >
Ok, thanks. Ding > Thanks, > > Ingo > > * Ding Tianhong <[email protected]> wrote: > >> I build a script to create several process for ioctl loop calling, >> the ioctl will calling the kernel function just like: >> xx_ioctl { >> ... >> rtnl_lock(); >> function(); >> rtnl_unlock(); >> ... >> } >> The function may sleep several ms, but will not halt, at the same time >> another user service may calling ifconfig to change the state of the >> ethernet, and after several hours, the hung task thread report this problem: >> >> ======================================================================== >> 149738.039038] INFO: task ifconfig:11890 blocked for more than 120 seconds. >> [149738.040597] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables >> this message. >> [149738.042280] ifconfig D ffff88061ec13680 0 11890 11573 0x00000080 >> [149738.042284] ffff88052449bd40 0000000000000082 ffff88053a33f300 >> ffff88052449bfd8 >> [149738.042286] ffff88052449bfd8 ffff88052449bfd8 ffff88053a33f300 >> ffffffff819e6240 >> [149738.042288] ffffffff819e6244 ffff88053a33f300 00000000ffffffff >> ffffffff819e6248 >> [149738.042290] Call Trace: >> [149738.042300] [<ffffffff8160d219>] schedule_preempt_disabled+0x29/0x70 >> [149738.042303] [<ffffffff8160af65>] __mutex_lock_slowpath+0xc5/0x1c0 >> [149738.042305] [<ffffffff8160a3cf>] mutex_lock+0x1f/0x2f >> [149738.042309] [<ffffffff8150d945>] rtnl_lock+0x15/0x20 >> [149738.042311] [<ffffffff81514e3a>] dev_ioctl+0xda/0x590 >> [149738.042314] [<ffffffff816121cc>] ? __do_page_fault+0x21c/0x560 >> [149738.042318] [<ffffffff814e42c5>] sock_do_ioctl+0x45/0x50 >> [149738.042320] [<ffffffff814e49d0>] sock_ioctl+0x1f0/0x2c0 >> [149738.042324] [<ffffffff811dc9b5>] do_vfs_ioctl+0x2e5/0x4c0 >> [149738.042327] [<ffffffff811e6a00>] ? fget_light+0xa0/0xd0 >> >> ================================ cut here ================================ >> >> I got the vmcore and found that the ifconfig is already in the wait_list of >> the >> rtnl_lock for 120 second, but my process could get and release the rtnl_lock >> normally several times in one second, so it means that my process jump the >> queue and the ifconfig couldn't get the rtnl all the time, I check the mutex >> lock >> slow path and found that the mutex may spin on owner ignore whether the >> wait list >> is empty, it will cause the task in the wait list always be cut in line, so >> add >> test for wait list in the mutex_can_spin_on_owner and avoid this problem. >> >> Signed-off-by: Ding Tianhong <[email protected]> >> --- >> kernel/locking/mutex.c | 11 ++++++----- >> 1 file changed, 6 insertions(+), 5 deletions(-) >> >> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c >> index 0551c21..596b341 100644 >> --- a/kernel/locking/mutex.c >> +++ b/kernel/locking/mutex.c >> @@ -256,7 +256,7 @@ static inline int mutex_can_spin_on_owner(struct mutex >> *lock) >> struct task_struct *owner; >> int retval = 1; >> >> - if (need_resched()) >> + if (need_resched() || atomic_read(&lock->count) == -1) >> return 0; >> >> rcu_read_lock(); >> @@ -283,10 +283,11 @@ static inline bool mutex_try_to_acquire(struct mutex >> *lock) >> /* >> * Optimistic spinning. >> * >> - * We try to spin for acquisition when we find that the lock owner >> - * is currently running on a (different) CPU and while we don't >> - * need to reschedule. The rationale is that if the lock owner is >> - * running, it is likely to release the lock soon. >> + * We try to spin for acquisition when we find that there are no >> + * pending waiters and the lock owner is currently running on a >> + * (different) CPU and while we don't need to reschedule. The >> + * rationale is that if the lock owner is running, it is likely >> + * to release the lock soon. >> * >> * Since this needs the lock owner, and this mutex implementation >> * doesn't track the owner atomically in the lock field, we need to >> -- >> 2.5.0 >> >> > > . >
