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    SubjectRe: arca-vm-8 [Re: [patch] arca-vm-6, killed kswapd [Re: [patch] new-vm , improvement , [Re: 2.2.0 Bug summary]]]
    On Thu, 7 Jan 1999, Linus Torvalds wrote:

    > Ok, here it is.. Stable.

    Yesterday after your email I tried and I been able to reproduce the
    deadlock here too. It's trivial, simply alloc a shared mapping of 160Mbyte
    and start dirtifying it and msync it in loop. So I applyed your patch and
    the machine still deadlocked after some second. I thought "argg
    update_shared_mappings is faulting noooooo"!! So I removed
    updated_shared_mappings() and I tried again and it still deadlocked... I
    thought "oh, cool, I still have something to fix ;)".

    So I developed this debugging code (that I post here because I guess it
    could be useful also to many others) to know which was the still pending

    Index: sched.c
    RCS file: /var/cvs/linux/kernel/sched.c,v
    retrieving revision
    diff -u -r1. sched.c
    --- sched.c 1999/01/07 11:57:23
    +++ sched.c 1999/01/08 10:41:53
    @@ -22,6 +22,10 @@
    * current-task

    + * Debug down() code. Copyright (C) 1999 Andrea Arcangeli
    + */
    #include <linux/mm.h>
    #include <linux/kernel_stat.h>
    #include <linux/fdreg.h>
    @@ -893,12 +897,27 @@
    tsk->state = TASK_RUNNING; \
    remove_wait_queue(&sem->wait, &wait);

    +void generate_oops (struct semaphore *sem)
    + sema_init(sem, 9876);
    + wake_up(&sem->wait);
    void __down(struct semaphore * sem)
    + struct timer_list timer;
    + init_timer (&timer);
    + timer.expires = jiffies + HZ*20;
    + = (unsigned long) sem;
    + timer.function = (void (*)(unsigned long)) generate_oops;
    + add_timer(&timer);
    + if (atomic_read(&sem->count) == 9876)
    + *(int *) 0 = 0;
    + del_timer(&timer);

    int __down_interruptible(struct semaphore * sem)

    Then recompiled, rebooted, return to run the deadlocking proggy, deadlocked
    again after some seconds and after 20 second I had a
    nice Oops on the screen. SysRQ-K helped me to restore some functionality
    in another console. Then I run dmesg | ksymoops.... and I had this:
    Using `/usr/src/linux/' to map addresses to symbols.

    >>EIP: c0111646 <__down+b2/160>
    Trace: c0111574 <generate_oops>
    Trace: c0189f58 <__down_failed+8/10>
    Trace: c010ef1a <do_page_fault+56/340>
    Trace: c0108c0d <error_code+2d/40>
    Trace: c0111646 <__down+b2/160>
    Trace: c0111574 <generate_oops>
    Trace: c0189f58 <__down_failed+8/10>
    Trace: c011dc59 <filemap_write_page+9d/138>
    Trace: c011dd59 <filemap_swapout+65/7c>
    Trace: c0121864 <try_to_swap_out+118/1c4>
    Trace: c0121a18 <swap_out_vma+108/164>
    Trace: c0121ad4 <swap_out_process+60/88>
    Trace: c0121bdb <swap_out+df/fc>
    Trace: c011cbb7 <shrink_mmap+11b/138>
    Trace: c0121d1a <free_user_and_cache+1e/34>
    Trace: c0121d76 <try_to_free_pages+46/a4>
    Trace: c0122615 <__get_free_pages+d5/220>
    Trace: c0126af2 <get_hash_table+52/64>
    Trace: c0127bcf <grow_buffers+3b/ec>
    Trace: c0126ca8 <refill_freelist+c/34>
    Trace: c0126f3a <getblk+202/228>
    Trace: c013af6c <ext2_alloc_block+68/13c>
    Trace: c013b5c4 <block_getblk+15c/2b0>
    Trace: c013b887 <ext2_getblk+16f/20c>
    Trace: c0139d2b <ext2_file_write+40b/554>
    Trace: c011dcc0 <filemap_write_page+104/138>
    Trace: c011e0fe <filemap_sync+256/30c>
    Trace: c011e297 <msync_interval+2f/7c>
    Trace: c011e3d2 <sys_msync+ee/14c>
    Trace: c0108ad4 <system_call+34/40>
    Code: c0111646 <__down+b2/160>
    Code: c0111646 <__down+b2/160> c7 05 00 00 00 movl $0x0,0x0
    Code: c011164b <__down+b7/160> 00 00 00 00 00
    Code: c0111656 <__down+c2/160> 8b 75 d8 movl 0xffffffd8(%ebp),%esi
    Code: c0111659 <__down+c5/160> c7 06 02 00 00 movl $0x2,(%esi)
    Code: c011165f <__down+cb/160> 31 00 xorl %eax,(%eax)
    Code: c0111667 <__down+d3/160> 90 nop
    Code: c0111668 <__down+d4/160> 90 nop
    Code: c0111669 <__down+d5/160> 90 nop
    So I looked at buffer.c ;)

    Index: buffer.c
    RCS file: /var/cvs/linux/fs/buffer.c,v
    retrieving revision
    diff -u -r1. buffer.c
    --- buffer.c 1999/01/07 11:57:21
    +++ linux/fs/buffer.c 1999/01/08 10:27:09
    @@ -689,7 +689,7 @@
    static void refill_freelist(int size)
    - if (!grow_buffers(GFP_KERNEL, size)) {
    + if (!grow_buffers(GFP_BUFFER, size)) {
    current->policy |= SCHED_YIELD;

    and now is really stable ;))

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