[OpenAFS-devel] locking fairness on Linux?

[Chaskiel M Grundman]

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--On Saturday, May 07, 2005 01:36:24 PM -0400 "John S. Bucy"=20
<bucy-openafs-devel@gloop.org> wrote:

> Here's what I got.  I can't make much of it and it seems a little
> garbled.  PID 8715 is starving and PID 8716 is running.
That's backwards of how I interpret things, actually. 8715 is in the rx=20
network code, waiting for a reply, and 8716 seems to be in=20
down(&dir->i_sem) in real_lookup (inlined in do_lookup).

I've cleaned up the traces below. The output you get from the kernel is not =

a true stack trace (unless frame pointers are enabled), but a listing of=20
all the kernel text addresses found on the stack. I'm not sure why so much=20
stuff is left on the stack, but it is.

> statnr-rate   S C03CDC88     0  8715   8700                     (NOTLB)
>  [<d8abde04>] afs_osi_SleepSig+0xb4/0xf0 [libafs]
>  [<d8abde8d>] afs_osi_Sleep+0x4d/0x80 [libafs]
>  [<d8aaf347>] rxi_ReadProc+0xe7/0x470 [libafs]
>  [<d8aaf820>] rx_ReadProc32+0x80/0xe0 [libafs]
>  [<d8ab468a>] xdrrx_getint32+0x1a/0x40 [libafs]
>  [<d8aa2f2e>] xdr_afs_uint32+0x3e/0x40 [libafs]
>  [<d8aa0f8f>] xdr_AFSFetchStatus+0x1f/0x220 [libafs]
>  [<d8aa360a>] RXAFS_FetchStatus+0x17a/0x1c0 [libafs]
>  [<d8a8bf2c>] afs_FetchStatus+0xbc/0x580 [libafs]
>  [<d8a8a7a4>] afs_GetVCache+0x2b4/0x510 [libafs]
>  [<d8a95837>] afs_lookup+0xd07/0x13f0 [libafs]
>  [<d8ac09a7>] afs_linux_lookup+0x37/0x140 [libafs]
>  [<c0157271>] real_lookup+0xc1/0xf0
>  [<c0157506>] do_lookup+0x96/0xb0
>  [<c0157aad>] link_path_walk+0x58d/0xb10
>  [<c015827e>] path_lookup+0x6e/0x120
>  [<c01584f3>] __user_walk+0x33/0x60
>  [<c015335f>] vfs_stat+0x1f/0x60
>  [<c0153aab>] sys_stat64+0x1b/0x40
>  [<c0102493>] syscall_call+0x7/0xb
> statnr-rate   D C03CD7E0     0  8716   8706                     (NOTLB)
> cc8ede08 00000082 d6305510 c03cd7e0 cc8ede30 00000008 d8a8cfd2 d6393800
>  [<c02cfaab>] __down+0x7b/0xd0
>  [<c02cfbff>] __down_failed+0x7/0xc
>  [<c015ab4b>] .text.lock.namei+0x8/0x1dd
>  [<c0157506>] do_lookup+0x96/0xb0
>  [<c0157aad>] link_path_walk+0x58d/0xb10
>  [<c015827e>] path_lookup+0x6e/0x120
>  [<c01584f3>] __user_walk+0x33/0x60
>  [<c015335f>] vfs_stat+0x1f/0x60
>  [<c0153aab>] sys_stat64+0x1b/0x40
>  [<c01d6112>] copy_to_user+0x42/0x60
>  [<c0102493>] syscall_call+0x7/0xb

I got similar results, as well as the following stack from an ls
ls            D C03605E0     0 20998   3600                     (NOTLB)
 [<c0281f95>] __down+0x95/0x110
 [<c0282158>] __down_failed+0x8/0xc
 [<c016839f>] .text.lock.readdir+0x5/0x16
 [<c016835e>] sys_getdents64+0x6e/0xaa
 [<c0105fe9>] sysenter_past_esp+0x52/0x71

Which is presumably down(&inode->i_sem) in vfs_readdir()  (the only down in =

readdir.c)

I can't say why the threads aren't switching off the way they should, but=20
it's not afs's fault.

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