On Wed, Sep 23, 2015 at 06:13:54PM +0900, Sergey Senozhatsky wrote: > On (09/23/15 11:06), Vladimir Davydov wrote: > > Hi, > > > > On Tue, Sep 22, 2015 at 04:30:13PM -0700, David Rientjes wrote: > > > The oom killer takes task_lock() in a couple of places solely to protect > > > printing the task's comm. > > > > > > A process's comm, including current's comm, may change due to > > > /proc/pid/comm or PR_SET_NAME. > > > > > > The comm will always be NULL-terminated, so the worst race scenario would > > > only be during update. We can tolerate a comm being printed that is in > > > the middle of an update to avoid taking the lock. > > > > > > Other locations in the kernel have already dropped task_lock() when > > > printing comm, so this is consistent. > > > > Without the protection, can't reading task->comm race with PR_SET_NAME > > as described below? > > the previous name was already null terminated, Yeah, but if the old name is shorter than the new one, set_task_comm() overwrites the terminating null of the old name before writing the new terminating null, so there is a short time window during which tsk->comm might be not null-terminated, no? Thanks, Vladimir > so it should be > > [name\0old_name\0] > > -ss > > > > > Let T->comm[16] = "name\0rubbish1234" > > > > CPU1 CPU2 > > ---- ---- > > set_task_comm(T, "longname\0") > > T->comm[0] = 'l' > > T->comm[1] = 'o' > > T->comm[2] = 'n' > > T->comm[3] = 'g' > > T->comm[4] = 'n' > > printk("%s\n", T->comm) > > T->comm = "longnrubbish1234" > > OOPS: the string is not > > nil-terminated! > > T->comm[5] = 'a' > > T->comm[6] = 'm' > > T->comm[7] = 'e' > > T->comm[8] = '\0' > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>