Messages in this thread | | | Date | Wed, 23 Sep 2015 18:13:54 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [patch] mm, oom: remove task_lock protecting comm printing |
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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, 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'
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