From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 30530 invoked by alias); 17 Oct 2007 15:11:10 -0000 Received: (qmail 30479 invoked by uid 48); 17 Oct 2007 15:10:51 -0000 Date: Wed, 17 Oct 2007 15:11:00 -0000 From: "matt dot hoosier at gmail dot com" To: glibc-bugs@sources.redhat.com Message-ID: <20071017151048.5192.matt.hoosier@gmail.com> Reply-To: sourceware-bugzilla@sourceware.org Subject: [Bug nptl/5192] New: Internal lock in pthread struct is vulnerable to priority inversion X-Bugzilla-Reason: CC Mailing-List: contact glibc-bugs-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: glibc-bugs-owner@sourceware.org X-SW-Source: 2007-10/txt/msg00113.txt.bz2 When most public API operations on pthread_t's execute, the per-thread lock (struct pthread.lock) is acquired to enforce consistency of the kernel and userspace data structures. This can cause a problem when a thread (t1) lowers its own priority and some other thread (t2, high priority) then immediately becomes runnable as a result of the priority shift. The scenario would look like this: * There are three threads: T1 (low prio), T2 (mid prio), T3 (high prio) * T1 is initially running at some value higher than its permanent priority, to do some startup work * T2 is executing some CPU-bound job that is always runnable * T1 finishes initialization, sets itself to its lower (permanent) priority. This requires grabbing the locking its own per-thread futex ("lock" in struct pthread). The syscall to alter scheduling parameters will immediately result in T2 being put on the CPU, so the lock is not yet dropped. * T3 eventually needs to do some adjustment of T1's scheduling options. So it tries to grab T1's per-thread lock, but can't since T1 still holds it because its scheduling syscall hasn't returned to userspace yet. * Priority inversion. T2 continues to run unchallenged. Can the pthread.lock be treated as a PI futex instead of a standard futex, in order to get priority inheritance and work around this inversion? I'll attach an example program shortly. -- Summary: Internal lock in pthread struct is vulnerable to priority inversion Product: glibc Version: unspecified Status: NEW Severity: normal Priority: P2 Component: nptl AssignedTo: drepper at redhat dot com ReportedBy: matt dot hoosier at gmail dot com CC: glibc-bugs at sources dot redhat dot com GCC build triplet: i686-pc-linux-gnu GCC host triplet: arm-none-linux-gnueabi http://sourceware.org/bugzilla/show_bug.cgi?id=5192 ------- You are receiving this mail because: ------- You are on the CC list for the bug, or are watching someone who is.