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Date: Thu, 21 May 2020 22:26:29 -0400
From: "dalias@aerifal.cx" <dalias@aerifal.cx>
To: tangyizhou <tangyizhou@huawei.com>
Cc: "musl@lists.openwall.com" <musl@lists.openwall.com>,
	"Wanghui (John)" <john.wanghui@huawei.com>,
	"Huangshuai (OSLab)" <elvis.huang@huawei.com>
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User-Agent: Mutt/1.5.21 (2010-09-15)
Subject: Re: [musl] Fix the return value of pthread_getschedparam in musl libc

On Fri, May 22, 2020 at 01:53:02AM +0000, tangyizhou wrote:
> > What is the situation under which SYS_sched_getparam can succeed
> > but SYS_sched_getscheduler can fail? The Linux man page
> > documenting the syscall:
> 
> There is a timing issue between two syscalls. Think about a concurrent scenario:
> Thread A calls pthread_getschedparam() to query the information of
> thread B.. After SYS_sched_getparam succeeds and before
> SYS_sched_getscheduler starts, thread B is killed, then
> SYS_sched_getparam returns -ESRCH.

There's not such an issue. t->killlock is held so that this can't
happen, and more importantly, so that the thread can't exit and the
tid be reassigned to a new thread or process that would wrongly be
acted upon.

Rich