Date: Tue, 22 Oct 2019 13:44:34 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Andriy Gapon <avg@FreeBSD.org> Cc: FreeBSD Current <freebsd-current@FreeBSD.org> Subject: Re: thread on sleepqueue does not wake up after timeout Message-ID: <20191022104434.GM73312@kib.kiev.ua> In-Reply-To: <aff7b1e5-c380-9d86-d638-047e618894e6@FreeBSD.org> References: <aff7b1e5-c380-9d86-d638-047e618894e6@FreeBSD.org>
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On Tue, Oct 22, 2019 at 01:08:59PM +0300, Andriy Gapon wrote: > > We observe a problem that happens very rarely (about once a month across many > test machines). The problem is that a thread remain in sleepq_timedwait() even > after its timeout expires. The thread's td_slpcallout looks like the callout > has fired. But the thread's state looks like it was never notified. > E.g.: > (kgdb) p td->td_slpcallout > $1 = {c_links = {le = {le_next = 0xfffff800108e6470, le_prev = > 0xfffffe0000be6ea8}, sle = {sle_next = 0xfffff800108e6470}, tqe = {tqe_next = > 0xfffff800108e6470, tqe_prev = 0xfffffe0000be6ea8}}, c_time = 160957479343159, > c_precision = 268435450, c_arg = 0xfffff80184602000, c_func = > 0xffffffff807481d0 <sleepq_timeout>, c_lock = 0x0, c_flags = 2, c_iflags = 272, > c_cpu = 6, c_exec_time = 160957506517070} [*] > (kgdb) p/x td->td_flags > $5 = 0x80000004 What is the bit 31 in your flags ? FreeBSD does not use the bit. > (kgdb) p td->td_sqqueue > $8 = 0 > (kgdb) p td->td_sleepqueue > $9 = (struct sleepqueue *) 0x0 > (kgdb) p td->td_wchan > $10 = (void *) 0xfffff802b990df38 > > > Has anyone seen anything like this problem? Yes, but it was very long time ago. See r303426. > Any advice on how to diagnose it? > > Thanks! > > P.S. > c_exec_time is our addition, we set this field right before firing a callback > and we reset it to zero when a callout is (re-)scheduled.
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