Re: pagefault in generic_file_buffered_write() causing deadlock

[Badari Pulavarty <pbadari@us.ibm.com>]

Andrew Morton wrote:
> On Wed, 15 Nov 2006 07:57:45 -0800
> Badari Pulavarty <pbadari@us.ibm.com> wrote:
>
>   
>> We are looking at a customer situation (on 2.6.16-based distro) - where
>> system becomes almost useless while running some java & stress tests.
>>
>> Root cause seems to be taking a pagefault in generic_file_buffered_write
>> () after calling prepare_write. I am wondering 
>>
>> 1) Why & How this can happen - since we made sure to fault the user
>> buffer before prepare write.
>>     
>
> When using writev() we only fault in the first segment of the iovec.  If
> the second or succesive segment isn't mapped into pagetables we're
> vulnerable to the deadlock.
>
>   
Hmm.. Not it :(
Its coming from write() not writev().

[C00000002ABBF290] [C00000000039D58C] .do_page_fault+0x2e4/0x75c
[C00000002ABBF460] [C000000000004860] .handle_page_fault+0x20/0x54
--- Exception: 301 at .__copy_tofrom_user+0x11c/0x580
    LR = .generic_file_buffered_write+0x39c/0x7c8
[C00000002ABBF750] [C000000000095A94]
.generic_file_buffered_write+0x2c0/0x7c8 (
unreliable)
[C00000002ABBF8F0] [C0000000000962EC]
.__generic_file_aio_write_nolock+0x350/0x3
e0
[C00000002ABBFA20] [C000000000096908] .generic_file_aio_write+0x78/0x104
[C00000002ABBFAE0] [C0000000001649F0] .ext3_file_write+0x2c/0xd4
[C00000002ABBFB70] [C0000000000C5168] .do_sync_write+0xd4/0x130
[C00000002ABBFCF0] [C0000000000C5ED4] .vfs_write+0x128/0x20c
[C00000002ABBFD90] [C0000000000C664C] .sys_write+0x4c/0x8c
[C00000002ABBFE30] [C00000000000871C] syscall_exit+0x0/0x40

Thanks,
Badari