Date: Sun, 18 Feb 2018 09:28:30 +0200 From: Andriy Gapon <avg@FreeBSD.org> To: Gleb Smirnoff <glebius@FreeBSD.org> Cc: Andrew Reilly <areilly@bigpond.net.au>, kib@FreeBSD.org, current@FreeBSD.org Subject: Re: Since last week (today) current on my Ryzen box is unstable Message-ID: <431f3e00-c66a-8e2e-6c61-a315a6353d1d@FreeBSD.org> In-Reply-To: <20180218023545.GE93303@FreeBSD.org> References: <0CEA9D55-D488-42EC-BBDE-D0B7CE58BAEA@bigpond.net.au> <cc3ae685-5f0e-d968-7b08-60a4836093e1@FreeBSD.org> <20180218023545.GE93303@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On 18/02/2018 04:35, Gleb Smirnoff wrote: > Andriy, > > On Sun, Feb 18, 2018 at 12:54:21AM +0200, Andriy Gapon wrote: > A> > Today's rebuild has given me uptimes of below an hour, usually. The box will stay up in single user mode long enough to rebuild world/kernel, but multi-user it is panicking at /usr/src/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c:1592 > A> > > A> > The backtrace shows that it gets to this panic from a sendfile() syscall. The line above is in the middle of a big edit that's part of svn revision 329363. The tripping assertion seems to suggest that m->valid != 0, for whatever that's worth. > A> > A> I am doing a bit of an offline investigation with Andrew and it seems that the > A> actual panic message is this: > A> > A> panic: vm_page_assert_xbusied: page 0xfffff807ebbd8f98 not exclusive busy @ > A> /usr/src/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c:1592 > A> > A> The stack is this: > A> vpanic() at vpanic/frame 0xfffffe00b3c36390 > A> dmu_read_pages() at dmu_read_pages+0x535/frame 0xfffffe00b3c36460 > A> zfs_freebsd_getpages() at zfs_freebsd_getpages+0x24c/frame 0xfffffe00b3c36510 > A> VOP_GETPAGES_APV() at VOP_GETPAGES_APV+0xd9/frame 0xfffffe00b3c36540 > A> vop_stdgetpages_async() at vop_stdgetpages_async+0x49/frame 0xfffffe00b3c36590 > A> VOP_GETPAGES_ASYNC_APV() at VOP_GETPAGES_ASYNC_APV+0xd9/frame 0xfffffe00b3c365c0 > A> vnode_pager_getpages_async() at vnode_pager_getpages_async+0x81/frame > A> 0xfffffe00b3c36650 > A> vn_sendfile() at vn_sendfile+0xe70/frame 0xfffffe00b3c368e0 > A> sendfile() at sendfile+0x149/frame 0xfffffe00b3c36980 > A> amd64_syscall() at amd64_syscall+0x79b/frame 0xfffffe00b3c36ab0 > A> fast_syscall_common() at fast_syscall_common+0x101/frame 0x7fffffffdb00 > A> > A> I looked at sendfile_swapin() code and it seems that it uses the pager API in an > A> undocumented way. Specifically, it inserts bogus_page into the array of > A> requested pages. For starters, bogus_page is not busied and VOP_GETPAGES is > A> documented to have all requested pages exclusively busied. Second, I always had > A> an impression that bogus_page is an implementation detail of the unified buffer > A> / page cache and that other code need not be aware of it. > A> > A> So, my opinion is that the sendfile code uses a "clever hack" that happens to > A> work with the buffer cache based filesystems, but that that hack is a bug. > A> So, I'd prefer that the problem is fixed in that code. > A> But I am open to being convinced that all VOP_GETPAGES implementations, > A> including that in ZFS, must be made aware of bogus_page. Or, at least, that > A> they should not verify that the requested pages are busied. > > This is optimization that improves throughput when file memory cache is > fragmented. Why don't you like adding the code to zfs_freebsd_getpages()? I cited two reasons above and expected to hear some counter-points rather than them being ignored :-) If we settle upon allowing bogus_page to be used in ma[], then that will obviously need to be documented. -- Andriy Gapon
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?431f3e00-c66a-8e2e-6c61-a315a6353d1d>