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SubjectRe: PS hanging in 2.4.1 - HAPPENING NOW!!!


On Sat, 3 Feb 2001, Shawn.Starr@Home.net wrote:
>
>Feb 3 17:57:08 coredump kernel: gnomeicu S 0000CD17 0 9338 1 (NOTLB) 9340 9332
>Feb 3 17:57:08 coredump kernel: Call Trace: [search_by_key+203/3232] [search_for_position_by_key+170/916] [make_cpu_key+57/64] [_get_block_create_0+136/1072] [_get_block_create_0+162/1072] [remove_wait_queue+40/48] [__wait_on_buffer+128/140]
>Feb 3 17:57:08 coredump kernel: [<f0000000>] [reiserfs_get_block+158/3408] [search_for_position_by_key+170/916] [search_for_position_by_key+570/916] [make_cpu_key+57/64] [kmem_cache_alloc+75/116] [get_unused_buffer_head+52/144] [create_buffers+96/444]
>Feb 3 17:57:08 coredump kernel: [block_read_full_page+246/552] [add_to_page_cache_unique+202/212] [reiserfs_readpage+15/20] [reiserfs_get_block+0/3408] [read_cluster_nonblocking+258/324] [filemap_nopage+332/1032] [do_no_page+77/192] [handle_mm_fault+232/340]
>Feb 3 17:57:08 coredump kernel: [do_page_fault+312/1020] [do_page_fault+0/1020] [start_request+388/508] [intlat_local_irq_disable+16/20] [ide_do_request+685/752] [schedule+639/964] [remove_wait_queue+40/48] [error_code+52/64]
>Feb 3 17:57:09 coredump kernel: [__generic_copy_from_user+52/60] [opost_block+67/384] [handle_mm_fault+232/340] [add_wait_queue+59/68] [write_chan+365/516] [tty_write+341/448] [write_chan+0/516] [sys_write+143/196]
>Feb 3 17:57:09 coredump kernel: [system_call+62/80]

Ok, the above seems to be the culprit here.

Note how the thing is in TASK_INTERRUPTIBLE (S) sleep somewhere in the
reiserfs code..

Debugging this is slightly harder than I'd like, because the "call trace"
is really not a trace, but actually just a dump of the stack of everything
that looks like a kernel address. And a lot of it is crap - stuff left
over by previous calls that hasn't gotten overwritten and is visible
because some function has a large stack footprint (lots of local variables
that end up not being very used and let things show through).

Anyway, what I _think_ is the cleaned-up stacktrace is

[reiserfs_get_block+158/3408]
[reiserfs_readpage+15/20]
[read_cluster_nonblocking+258/324]
[filemap_nopage+332/1032]
[do_no_page+77/192]
[handle_mm_fault+232/340]
[do_page_fault+312/1020]
[error_code+52/64]
[__generic_copy_from_user+52/60]
[opost_block+67/384]
[handle_mm_fault+232/340]
[add_wait_queue+59/68]
[write_chan+365/516]
[tty_write+341/448]
[write_chan+0/516]
[sys_write+143/196]
[system_call+62/80]

and what is interesting is that you got a page fault while you were
copying stuff in to the tty layer. Which happens with TASK_INTERRUPTIBLE
sleep. Now, the page fault code never clears that, so we enter reiserfs
still "sleeping", and reiserfs will do a

if (need_resched(current))
schedule();
which won't do what reiserfs _wants_ it to do at all. Because if
task->state is TASK_INTERRUPTIBLE, the above will go to sleep, not just
cause a nice reschedule. And we'll be sleeping with the task MM semaphore
held - only to wake up if somebody were to signal us or something.

If you can re-create this hang, could you please try to add this single
line to the top of "handle_mm_fault()" in mm/memory.c (after the variable
declarations, of course):

current->state = TASK_RUNNING;

which just means that if we get a page fault while we're half asleep, it
will be safe to do a schedule() without explicitly setting the process
running again.

Linus

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