Additional analysis tools


Partway through the analysis of this system, it became apparent that this crash dump was going to present a bit of a puzzle. Sensing this, we resorted to a little-known trade secret among the kernel gurus. Yes, we grabbed a pad of paper and a pencil and started recording what we were finding.

The initial result is the table below.

 Thread         Mutex        Symbol Name         Owner  e18c9ec0      e00ecb34      poll_lock          f66d2800  e1bd8ec0      e00ecb34      poll_lock          f66d2800  f5ab7400      e00ecb34      poll_lock          f66d2800  f5a3ce00      e00ecb34      poll_lock          f66d2800  f6756000      e00ecb34      poll_lock          f66d2800  f57a1c00      e00ecb34      poll_lock          f66d2800  e1b6bec0      e00ecb34      poll_lock          f66d2800  f66d2800      f6080f4c       (none)            e190cec0  e190cec0      f5fbbcf4       (none)            f600ec00  f600ec00      f5fde918      abc_top_mutex      f66d2800  e18d2ec0      f5fde910      abc_last_mutex     f66d2800  f6226e00      f5490308       (none)            f572ee00 

After we stared at this for a few minutes, it seemed that this Dragon was stuck in what is called a "deadlock condition" or "deadlock chain." To confirm this, we went right back to the pad of paper and started drawing lines and circles, tracking the dependencies. In other words, we needed to see which processes were waiting for which locks which were owned by which processes which were waiting for which locks, and so on.

In the end, it turns out that the deadlock involved only three of the processes shown in the table, as drawn here. However, the nine other processes were "hung," waiting around for the deadlock to be resolved.

Figure 34-1. Deadlock Condition

graphics/34fig01.gif

How this deadlock condition was created is anyone 's guess. If the system administrator was patient, would the deadlock eventually be resolved? The answer is to that question is "No," thus the name deadlock .



PANIC. UNIX System Crash Dump Analysis Handbook
PANIC! UNIX System Crash Dump Analysis Handbook (Bk/CD-ROM)
ISBN: 0131493868
EAN: 2147483647
Year: 1994
Pages: 289
Authors: Chris Drake

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