Re: r340343 triggers kernel assertion if file is opened with O_BENEATH flag set through symlink

On Wed, Nov 28, 2018 at 01:46:17AM +0200, Konstantin Belousov wrote:
> On Wed, Nov 28, 2018 at 12:54:21AM +0300, Vladimir Kondratyev wrote:
> > Following test case triggers assertion after r340343:
> > 
> > 
> > #include <fcntl.h>
> > 
> > int
> > main(int argc, char **argv)
> > {
> >         openat(open("/etc", O_RDONLY), "termcap", O_RDONLY | O_BENEATH);
> > }
> > 
> > It results in:
> > 
> > panic: Assertion (ndp->ni_lcf & NI_LCF_LATCH) != 0 failed at
> > /usr/src/sys/kern/vfs_lookup.c:182
> > 
> 
> The following should fix it. Problem was that the topping directory was
> only latched when the initial path was absolute. Since your example
> switched from the relative argument to the absolute symlink, the BENEATH
> tracker rightfully complained that there were no recorded top.
> 
> I also added some asserts I used during the debugging.
> 
> diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c
> index 78893c4f2bd..7a80775d91d 100644
> --- a/sys/kern/vfs_lookup.c

With this patch I got a:

$ ./beneath.sh
open("a/b") succeeded
stat("a/b
panic: Assertion (ndp->ni_lcf & NI_LCF_LATCH) != 0 failed at ../../../kern/vfs_lookup.c:269
cpuid = 4
time = 1543397647
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe00c71881a0
vpanic() at vpanic+0x1a3/frame 0xfffffe00c7188200
panic() at panic+0x43/frame 0xfffffe00c7188260
namei_handle_root() at namei_handle_root+0xf7/frame 0xfffffe00c71882b0
namei() at namei+0x617/frame 0xfffffe00c71884f0
vn_open_cred() at vn_open_cred+0x526/frame 0xfffffe00c7188640
vn_open() at vn_open+0x4c/frame 0xfffffe00c7188680
kern_openat() at kern_openat+0x2e9/frame 0xfffffe00c71888e0
sys_openat() at sys_openat+0x69/frame 0xfffffe00c7188910
syscallenter() at syscallenter+0x4e3/frame 0xfffffe00c71889f0
amd64_syscall() at amd64_syscall+0x4d/frame 0xfffffe00c7188ab0
fast_syscall_common() at fast_syscall_common+0x101/frame 0xfffffe00c7188ab0
--- syscall (499, FreeBSD ELF64, sys_openat), rip = 0x8003a215a, rsp = 0x7fffffffe4f8, rbp = 0x7fffffffe5e0 ---

https://people.freebsd.org/~pho/stress/log/kostik1127.txt

- Peter