[Devel] Re: locking imbalance in restart error path

[Oren Laadan]

> Hi,
> 
> With ckpt-v19-dev I see the following complaint from lockdep when an
> error is detected.  This is from what I believe to be a legitimately
> failed restart attempt.  I guess releasing ctx->errno_sem in a task
> context different from the one in which it was acquired is causing this?

I think so. It's technically correct, but lockdep doesn't like it. I
recall discussing it on the IRC some time ago. We'll just have to use
some other sync mechanism instead, e.g. completion.

Oren.



> 
> (I have a couple patches from the list applied and some debugging code
> of my own, but they shouldn't affect this code.)
> 
> 
> [9145:9130:c/r:do_restore_tty:3073] sanity checks passed, link 0
> [err -16][pos 3297][E @ do_restore_tty:3083][pid -1 tsk NULL]Open ptmx
> =====================================
> [ BUG: bad unlock balance detected! ]
> -------------------------------------
> simple-wait/9145 is trying to release lock (&ctx->errno_sem) at:
> [<c000000000401bd0>] .ckpt_set_error+0x64/0x9c
> but there are no more locks to release!
> 
> other info that might help us debug this:
> no locks held by simple-wait/9145.
> 
> stack backtrace:
> Call Trace:
> [c000000002b12b70] [c000000000015350] .show_stack+0xc0/0x200 (unreliable)
> [c000000002b12c40] [c0000000007dc6a8] .dump_stack+0x28/0x3c
> [c000000002b12cc0] [c0000000000f897c] .print_unlock_inbalance_bug+0x110/0x13c
> [c000000002b12de0] [c0000000000f8d84] .lock_release+0x12c/0x228
> [c000000002b12e90] [c0000000000e2598] .up_write+0x3c/0x90
> [c000000002b12f20] [c000000000401bd0] .ckpt_set_error+0x64/0x9c
> [c000000002b12fb0] [c000000000401ca4] .do_ckpt_msg+0x9c/0xbc
> [c000000002b13050] [c0000000004951d8] .restore_tty+0x1a4/0x530
> [c000000002b13100] [c000000000403e84] .restore_obj+0x11c/0x1fc
> [c000000002b131b0] [c000000000406fd8] .ckpt_read_obj_dispatch+0x2dc/0x330
> [c000000002b13250] [c000000000407078] .ckpt_read_obj+0x4c/0x18c
> [c000000002b13310] [c0000000004072b4] .ckpt_read_buf_type+0x54/0xa8
> [c000000002b133b0] [c00000000040c568] .restore_file+0x44/0x174
> [c000000002b13450] [c000000000403e84] .restore_obj+0x11c/0x1fc
> [c000000002b13500] [c000000000406fd8] .ckpt_read_obj_dispatch+0x2dc/0x330
> [c000000002b135a0] [c000000000407078] .ckpt_read_obj+0x4c/0x18c
> [c000000002b13660] [c000000000407364] .ckpt_read_obj_type+0x5c/0x104
> [c000000002b13700] [c00000000040c1ac] .restore_file_table+0x164/0x4dc
> [c000000002b137f0] [c000000000403e84] .restore_obj+0x11c/0x1fc
> [c000000002b138a0] [c000000000406fd8] .ckpt_read_obj_dispatch+0x2dc/0x330
> [c000000002b13940] [c000000000407078] .ckpt_read_obj+0x4c/0x18c
> [c000000002b13a00] [c000000000407364] .ckpt_read_obj_type+0x5c/0x104
> [c000000002b13aa0] [c00000000040b12c] .restore_task+0x81c/0xd44
> [c000000002b13b50] [c000000000408d6c] .do_restart+0x1580/0x1a4c
> [c000000002b13cd0] [c000000000401110] .do_sys_restart+0xc4/0x108
> [c000000002b13d80] [c0000000000155e0] .sys_restart+0x64/0x94
> [c000000002b13e30] [c000000000008850] .ppc_restart+0x8/0x54
> [9143:1:c/r:wait_all_tasks_finish:1137] final sync kflags 0xa (ret 0)
> 
> 
> 
> 
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