Re: lock_kernel called under spinlock in NFS

[Joe Korty]

On Thu, Jun 01, 2006 at 04:13:39PM -0400, Trond Myklebust wrote:
> On Thu, 2006-06-01 at 15:55 -0400, Joe Korty wrote:
>> Tree 5fdccf2354269702f71beb8e0a2942e4167fd992
>> 
>>         [PATCH] vfs: *at functions: core
>> 
>> introduced a bug where lock_kernel() can be called from
>> under a spinlock.  To trigger the bug one must have
>> CONFIG_PREEMPT_BKL=y and be using NFS heavily.  It is
>> somewhat rare and, so far, haven't traced down the userland
>> sequence that causes the fatal path to be taken.
>> 
>> The bug was caused by the insertion into do_path_lookup()
>> of a call to file_permission().  do_path_lookup()
>> read-locks current->fs->lock for most of its operation.
>> file_permission() calls permission() which calls
>> nfs_permission(), which has one path through it
>> that uses lock_kernel().

> Nowhere should anyone be calling file_permission() under a spinlock.
> 
> Why would you need to read-protect current->fs in the case where you are
> starting from a file? The correct thing to do there would appear to be
> to read_protect only the cases where (*name=='/') and (dfd == AT_FDCWD).
> 
> Something like the attached patch...


Hi Trond,
I've been running with the patch for the last few hours, on an nfs-rooted
system, and it has been working fine.  Any plans to submit this for 2.6.17?

Thanks!!!
Joe
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