Date: Thu, 28 Feb 2008 15:04:55 +0100 From: "Attilio Rao" <attilio@freebsd.org> To: "Yuri Pankov" <yuri.pankov@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: pfind() in ithread handler Message-ID: <3bbf2fe10802280604t4266c0a9uaa0075689ce67632@mail.gmail.com> In-Reply-To: <20080228111222.GE92245@mail.irbisnet.ru> References: <20080228111222.GE92245@mail.irbisnet.ru>
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2008/2/28, Yuri Pankov <yuri.pankov@gmail.com>: > Hi, > > I'm trying to understand the cause of following panic. > > panic: Trying sleep, but thread marked as sleeping prohibited > cpuid = 0 > KDB: stack backtrace: > db_trace_self_wrapper() at db_trace_self_wrapper+0x2a > panic() at panic+0x17d > sleepq_add() at sleepq_add+0x2e1 > _sx_slock_hard() at _sx_slock_hard+0x15d > _sx_slock() at _sx_slock+0xc1 > pfind() at pfind+0x24 > saa_intr() at saa_intr+0x313 > ithread_loop() at ithread_loop+0xda > fork_exit() at fork_exit+0x12a > fork_trampoline() at fork_trampoline+0xe > --- trap 0, rip = 0, rsp = 0xffffffffac3c0d30, rbp = 0 --- > > Can someone enlighten me on what is causing the panic and is it ok to > use pfind() in interrupt handler (I have very limited understanding of > kernel internals)? > > Code in question (taken from saa driver > http://freebsd.ricin.com/ports/distfiles/kbtv-1.92.tbz) can be found at > http://www.pastebin.ca/921830 ithreads cannot perform unbound sleeps and pfind() needs to access to allproc_lock which is a sx lock and *performs* an unbound sleep, so there is a mismatch. Btw, it sounds like allproc_lock and other similar locks are just using an sx lock for *legacy*, they should be probabilly converted to rwlock. It also imposes little problems in the TTY layer, for example, where I saw you need to use a unbounded sleeping primitive because of processes locks acquisitions. A nice janitor task would be to convert these sx locks into rw and see what happens. Thanks, Attilio -- Peace can only be achieved by understanding - A. Einstein
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