Re: NFS swap on current appears to deadlock

[Andrew Doran <ad%netbsd.org@localhost>]

Hi,

Finally got around to trying this.  Having beaten on it for a while with
real hardware I don't see any problem with swapping over NFS on 9.99.63.

On Sat, May 02, 2020 at 12:06:48PM +1000, Paul Ripke wrote:

> I have a qemu guest for experimenting with -current, 1 CPU & 64MiB RAM.

64 megs, I'm surprised it makes to the login prompt.

Andrew

> I gave it an NFS swap space to cope with a few small builds, and it now
> locks up hard after touching that swap device.
> 
> >From ddb, stacks are like:
> 
> db{0}> t
> sched_resched_cpu() at netbsd:sched_resched_cpu+0x3f
> sleepq_wake() at netbsd:sleepq_wake+0x6c
> uvm_wait() at netbsd:uvm_wait+0x47
> uvn_findpage() at netbsd:uvn_findpage+0x21b
> uvn_findpages() at netbsd:uvn_findpages+0xca
> genfs_getpages() at netbsd:genfs_getpages+0x107a
> VOP_GETPAGES() at netbsd:VOP_GETPAGES+0x6b
> uvm_fault_internal() at netbsd:uvm_fault_internal+0x1aae
> trap() at netbsd:trap+0x521
> --- trap (number 6) ---
> c6c0bc1b:
> 
> db{0}> t
> binuptime() at netbsd:binuptime+0x79
> mi_switch() at netbsd:mi_switch+0x61
> sleepq_block() at netbsd:sleepq_block+0xb4
> mtsleep() at netbsd:mtsleep+0x137
> uvm_pageout() at netbsd:uvm_pageout+0x69e
> 
> They seem to change around, but userland in the OS seems pretty
> locked up. Running with the NFS swap space disabled, using a normal
> swap partition, is fine.
> 
> This is 9.99.56 amd64, btw.
> 
> Ideas?
> 
> Cheers,
> -- 
> Paul Ripke
> "Great minds discuss ideas, average minds discuss events, small minds
>  discuss people."
> -- Disputed: Often attributed to Eleanor Roosevelt. 1948.