Date: Tue, 21 Jul 2015 22:16:01 -0700 From: Adrian Chadd <adrian.chadd@gmail.com> To: Mateusz Guzik <mjguzik@gmail.com> Cc: John Baldwin <jhb@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r285125 - in head/sys: kern sys Message-ID: <CAJ-VmonVBqwh9gJHi4gj=NXxvMOh3Of%2B4-6hhaYYSvQUAHDg6Q@mail.gmail.com> In-Reply-To: <20150722043323.GA23614@dft-labs.eu> References: <201507040654.t646sGO7044196@repo.freebsd.org> <CAJ-VmokSbajFxOKPU=u4AQgPmtPqJXvzfbp4%2Bhrcd-PsCYq7PA@mail.gmail.com> <20150721083922.GB6736@dft-labs.eu> <3863130.vz23U50G0A@ralph.baldwin.cx> <20150722043323.GA23614@dft-labs.eu>
next in thread | previous in thread | raw e-mail | index | archive | help
Hi,
Test it out and then give me a patch. I'll go sacrifice this laptop to
the testing gods.
Thanks!
-a
On 21 July 2015 at 21:33, Mateusz Guzik <mjguzik@gmail.com> wrote:
> On Tue, Jul 21, 2015 at 11:50:12AM -0700, John Baldwin wrote:
>> On Tuesday, July 21, 2015 10:39:22 AM Mateusz Guzik wrote:
>> > Cc'ing jhb@ who made relevant changes to rmlocks
>> >
>> > On Mon, Jul 20, 2015 at 11:21:30PM -0700, Adrian Chadd wrote:
>> > > this happend whilst doing 'sysctl -vmstat 1' in one window, 'top' in
>> > > another window, and 'kldunload uhci' as root:
>> > >
>> > > Unread portion of the kernel message buffer:
>> > > uhci5: detached
>> > > panic: sleepq_add: td 0xc75d06a0 to sleep on wchan 0xc0b3e8e4 with
>> > > sleeping prohibited
>> > >
>> > [..]
>> >
>> > > #10 0xc06a882c in kassert_panic (fmt=<value optimized out>) at
>> > > /usr/home/adrian/work/freebsd/head/src/sys/kern/kern_shutdown.c:634
>> > > #11 0xc06f449b in sleepq_add (wchan=0xc0b3e8e4, wmesg=<value optimized
>> > > out>, flags=<value optimized out>, queue=<value optimized out>) at
>> > > /usr/home/adrian/work/freebsd/head/src/sys/kern/subr_sleepqueue.c:308
>> > > #12 0xc06b167b in _sx_xlock_hard (sx=0xc0b3e8e4, tid=<value optimized
>> > > out>, opts=<value optimized out>, file=0x0, line=18) at
>> > > /usr/home/adrian/work/freebsd/head/src/sys/kern/kern_sx.c:697
>> > > #13 0xc06b0841 in _sx_xlock (sx=0xc0b3e8e4, opts=<value optimized
>> > > out>, file=0xc09f2d35
>> > > "/usr/home/adrian/work/freebsd/head/src/sys/kern/kern_rmlock.c",
>> > > line=411) at sx.h:154
>> > > #14 0xc06a4510 in _rm_rlock (rm=0xc0b3e8cc, tracker=0xeaa61ad0,
>> > > trylock=<value optimized out>) at
>> > > /usr/home/adrian/work/freebsd/head/src/sys/kern/kern_rmlock.c:411
>> > > #15 0xc06a4e2d in _rm_rlock_debug (rm=0xc0b3e8cc, tracker=0xeaa61ad0,
>> > > trylock=0) at /usr/home/adrian/work/freebsd/head/src/sys/kern/kern_rmlock.c:665
>> > > #16 0xc06b5da4 in sysctl_root_handler_locked (oid=0xc0a6ee20,
>> > > arg1=<value optimized out>, arg2=<value optimized out>, req=<value
>> > > optimized out>, tracker=0xeaa61ad0) at
>> > > /usr/home/adrian/work/freebsd/head/src/sys/kern/kern_sysctl.c:170
>> > > #17 0xc06b5531 in sysctl_root (arg1=<value optimized out>, arg2=<value
>> > > optimized out>) at
>> > > /usr/home/adrian/work/freebsd/head/src/sys/kern/kern_sysctl.c:1692
>> > > #18 0xc06b5ac2 in userland_sysctl (td=<value optimized out>,
>> > > name=<value optimized out>, namelen=2, old=<value optimized out>,
>> > > oldlenp=<value optimized out>, inkernel=<value optimized out>,
>> > > new=<value optimized out>, newlen=<value optimized out>, retval=0x12,
>> > > flags=<value optimized out>) at
>> > > /usr/home/adrian/work/freebsd/head/src/sys/kern/kern_sysctl.c:1797
>> > > #19 0xc06b5908 in sys___sysctl (uap=0xeaa61ca8) at
>> > > /usr/home/adrian/work/freebsd/head/src/sys/kern/kern_sysctl.c:1724
>> > > #20 0xc096aaee in syscall (frame=<value optimized out>) at subr_syscall.c:133
>> > > #21 0xc0955c5c in Xint0x80_syscall () at
>> > > /usr/home/adrian/work/freebsd/head/src/sys/i386/i386/exception.s:278
>> >
>> > rmlock(9) states:
>> > Sleepable read-mostly locks are created by passing RM_SLEEPABLE to
>> > rm_init_flags(). Unlike normal read-mostly locks, sleepable read-mostly
>> > locks follow the same lock ordering rules as sx(9) locks. Sleepable
>> > read-mostly locks do not propagate priority to writers, but they do
>> > propagate priority to readers. Writers are permitted to sleep while
>> > holding a read-mostly lock, but readers are not. Unlike other sleepable
>> > locks such as sx(9) locks, readers must use try operations on other
>> > sleepable locks to avoid sleeping.
>> >
>> > May be that's my bad English, but I read that:
>> > rm_rlock(...);
>> > /* can't sleep here */
>> > rm_runlock(...);
>>
>> That is correct.
>>
>> > Turns out it's the rm_rlock itself which must not sleep and you have to
>> > rm_try_rlock instead.
>>
>> Hmm, I think instead, the THREAD_NO_SLEEPING in rm_rlock() just needs to
>> be moved. Or rather, rm_rlock_hard() needs to do THREAD_SLEEPING_OK
>> around the sx_xlock and then THREAD_NO_SLEEPING afterwards. Something
>> like this:
>>
>> Index: kern/kern_rmlock.c
>> ===================================================================
>> --- kern/kern_rmlock.c (revision 284344)
>> +++ kern/kern_rmlock.c (working copy)
>> @@ -407,9 +407,11 @@
>> return (0);
>> }
>> } else {
>> - if (rm->lock_object.lo_flags & LO_SLEEPABLE)
>> + if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
>> + THREAD_SLEEPING_OK();
>> sx_xlock(&rm->rm_lock_sx);
>> - else
>> + THREAD_NO_SLEEPING();
>> + } else
>> mtx_lock(&rm->rm_lock_mtx);
>> }
>>
>
> Works for me, I was reluctant to do this myself, hence the "wrapper"
> approach.
>
> Thanks.
>
> --
> Mateusz Guzik <mjguzik gmail.com>
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAJ-VmonVBqwh9gJHi4gj=NXxvMOh3Of%2B4-6hhaYYSvQUAHDg6Q>