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    SubjectRe: Fw: 2.5.61 oops running SDET
    > Close, but you also need
    >
    > - buffer = task_sig(task, buffer);
    > + if (task->sighand)
    > + buffer = task_sig(task, buffer);
    >
    > to actually check whether signals exist or not. Otherwise you'll just get
    > the same oops anyway (well, keeping the task locked may change timings
    > enough that it doesn't happen, but the bug will continue to be there.
    >
    > I would also say that since you explicitly take the task lock, there's no
    > real reason to use "get_task_mm()" at all any more, so instead of doing
    > that (and then doing the mmput()), just get rid of the mm variable
    > entirely, and do
    >
    > if (task->mm)
    > buffer = task_mem(task->mm, buffer)
    >
    > too. There's really no downside to just holding on to the task lock over
    > the whole operation instead of incrementing and decrementing the mm
    > counts and dropping the lock early.
    >
    > (There are a few valid reasons for using the "get_task_mm()" function:
    >
    > - you need to block and thus drop the task lock
    >
    > - the original code just used "task->mm" directly, and using
    > "get_task_mm()" made the original conversion to mm safe handling
    > easier.
    >
    > Neither reason is really valid any more in this function at least).

    OK, I did the following, which is what I think you wanted, plus Zwane's
    observation that task_state acquires the task_struct lock (we're the only
    caller, so I just removed it), but I still get the same panic and this time
    the box hung. No doubt I've just done something stupid in the patch ...
    (task_state takes the tasklist_lock ... is that safe to do inside task_lock?)

    diff -urpN -X /home/fletch/.diff.exclude virgin/fs/proc/array.c sdet/fs/proc/array.c
    --- virgin/fs/proc/array.c Sat Feb 15 16:11:45 2003
    +++ sdet/fs/proc/array.c Sat Feb 15 19:28:34 2003
    @@ -166,12 +166,10 @@ static inline char * task_state(struct t
    p->uid, p->euid, p->suid, p->fsuid,
    p->gid, p->egid, p->sgid, p->fsgid);
    read_unlock(&tasklist_lock);
    - task_lock(p);
    buffer += sprintf(buffer,
    "FDSize:\t%d\n"
    "Groups:\t",
    p->files ? p->files->max_fds : 0);
    - task_unlock(p);

    for (g = 0; g < p->ngroups; g++)
    buffer += sprintf(buffer, "%d ", p->groups[g]);
    @@ -243,20 +241,20 @@ extern char *task_mem(struct mm_struct *
    int proc_pid_status(struct task_struct *task, char * buffer)
    {
    char * orig = buffer;
    - struct mm_struct *mm = get_task_mm(task);

    + task_lock(task);
    buffer = task_name(task, buffer);
    buffer = task_state(task, buffer);

    - if (mm) {
    - buffer = task_mem(mm, buffer);
    - mmput(mm);
    - }
    - buffer = task_sig(task, buffer);
    + if (task->mm)
    + buffer = task_mem(task->mm, buffer);
    + if (task->sighand)
    + buffer = task_sig(task, buffer);
    buffer = task_cap(task, buffer);
    #if defined(CONFIG_ARCH_S390)
    buffer = task_show_regs(task, buffer);
    #endif
    + task_unlock(task);
    return buffer - orig;
    }



    Unable to handle kernel NULL pointer dereference at virtual address 00000014
    printing eip:
    c0118b13
    *pde = 2d4bf001
    *pte = 00000000
    Oops: 0000
    CPU: 6
    EIP: 0060:[<c0118b13>] Not tainted
    EFLAGS: 00010207
    EIP is at render_sigset_t+0x17/0x7c
    eax: 00000010 ebx: ed3d909f ecx: ed3d9097 edx: eda60100
    esi: 0000003c edi: 00000010 ebp: ed49bf04 esp: ed49bef8
    ds: 007b es: 007b ss: 0068
    Process ps (pid: 3339, threadinfo=ed49a000 task=ee32cd20)
    Stack: ed3d907d 00000002 ed3d909f 00000006 c016d85f 00000010 ed3d909f ed3d9097
    c0233f38 eda606bc ed3d9086 ed3d907e c0233f2f ee1d7b70 eda60100 eeb4d0c0
    ed3d9000 ee1d7b70 00000000 ed3d9000 000000d0 eeb4d0c0 c01300f6 c17119e8
    Call Trace:
    [<c016d85f>] proc_pid_status+0x26f/0x334
    [<c01300f6>] __get_free_pages+0x4e/0x54
    [<c016b517>] proc_info_read+0x53/0x130
    [<c0145295>] vfs_read+0xa5/0x128
    [<c0145522>] sys_read+0x2a/0x3c
    [<c0108b3f>] syscall_call+0x7/0xb
    Code: 0f a3 37 19 d2 b8 01 00 00 00 31 c9 85 d2 0f 45 c8 8d 56 01
    <1>Unable to handle kernel NULL pointer dereference at virtual address 00000014
    printing eip:
    c0118b13
    *pde = 2d512001
    *pte = 00000000
    Oops: 0000
    CPU: 2
    EIP: 0060:[<c0118b13>] Not tainted
    EFLAGS: 00010207
    EIP is at render_sigset_t+0x17/0x7c
    eax: 00000010 ebx: ee34b0a0 ecx: ee34b098 edx: ed3ea7a0
    esi: 0000003c edi: 00000010 ebp: ed54ff04 esp: ed54fef8
    ds: 007b es: 007b ss: 0068
    Process ps (pid: 14710, threadinfo=ed54e000 task=ee430d40)
    Stack: ee34b07e 00000002 ee34b0a0 00000006 c016d85f 00000010 ee34b0a0 ee34b098
    c0233f38 ed3ead5c ee34b087 ee34b07f c0233f2f ee4960d0 ed3ea7a0 eec66ca0
    ee34b000 ee4960d0 00000000 ee34b000 000000d0 eec66ca0 c01300f6 c17383b8
    Call Trace:
    [<c016d85f>] proc_pid_status+0x26f/0x334
    [<c01300f6>] __get_free_pages+0x4e/0x54
    [<c016b517>] proc_info_read+0x53/0x130
    [<c0145295>] vfs_read+0xa5/0x128
    [<c0145522>] sys_read+0x2a/0x3c
    [<c0108b3f>] syscall_call+0x7/0xb
    Code: 0f a3 37 19 d2 b8 01 00 00 00 31 c9 85 d2 0f 45 c8 8d 56 01

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