Solaris tip of the week: use mdb to view process stack

The solaris pstack command can be used to view most user process stacks, but I recently encountered a situation where even the pstack -F could not be used to view the process stack.

I issued a zfs recv operation that never returned.

# ps -ef | grep zfs

root 7485 7484 0 01:40:01 ? 0:00 zfs recv -F storage ...

# pstack -F 7485

[no output]

pstack could not grab control the process to display the stack.

My next option is to use mdb to view the stack - no quite as convenient as pstack, but more powerful ... here are the steps:

# mdb -k

/* get handle to the the zfs process using ::pgrep */

>::pgrep zfs

S PID PPID PGID SID UID FLAGS ADDR NAME
R 7485 7484 7484 7484 0 0x4a004000 ffffff278437ca88 zfs

/* use the returned ADDR value to get the process threadlist */

> ffffff278437ca88::threadlist
ADDR PROC LWP CMD/LWPID
ffffff278437ca88 ffffff21da3b68e0 0 /239

/* use the PROC value to view the stack */

> ffffff21da3b68e0::findstack
stack pointer for thread ffffff21da3b68e0: ffffff00f88fc880
[ ffffff00f88fc880 _resume_from_idle+0xf1() ]
ffffff00f88fc8b0 swtch+0x160()
ffffff00f88fc960 turnstile_block+0x764()
ffffff00f88fc9d0 rw_enter_sleep+0x1a3()
ffffff00f88fca40 dsl_dataset_clone_swap+0x61()
ffffff00f88fca90 dmu_recv_end+0x57()
ffffff00f88fcc40 zfs_ioc_recv+0x31e()
ffffff00f88fccc0 zfsdev_ioctl+0x10b()
ffffff00f88fcd00 cdev_ioctl+0x45()
ffffff00f88fcd40 spec_ioctl+0x83()
ffffff00f88fcdc0 fop_ioctl+0x7b()
ffffff00f88fcec0 ioctl+0x18e()
ffffff00f88fcf10 sys_syscall32+0x101()