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* [Bug 1001591] New: Bogus pseudo-randomness in garbage collect
@ 2012-05-21 13:02 bugzilla-daemon
2012-05-21 13:02 ` [Bug 1001591] Bogus pseudo-randomness in jffs2 " bugzilla-daemon
` (3 more replies)
0 siblings, 4 replies; 7+ messages in thread
From: bugzilla-daemon @ 2012-05-21 13:02 UTC (permalink / raw)
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Summary: Bogus pseudo-randomness in garbage collect
Product: eCos
Version: CVS
Platform: All
OS/Version: All
Status: UNCONFIRMED
Severity: major
Priority: low
Component: Filesystem support
AssignedTo: unassigned@bugs.ecos.sourceware.org
ReportedBy: stano@meduna.org
CC: ecos-bugs@ecos.sourceware.org
Class: Advice Request
The jffs2_find_gc_block function in fs/jffs2/current/src/gc.c and
jffs2_mark_node_obsolete in nodemgmt.c try to do pseudo-random stuff by
computing jiffies % 128 and making probability decisions on the result. First I
think that this kind of pseudo-randomness is not really correct for embedded
systems that often have very predictable execution times.
But what is much worse, compat/linux/current/include/linux/kernel.h defines
jiffies as
#define jiffies 100
I am no expert at jffs2 and cannot say whether this can lead to major problems
or not, so I'd like someone with better understanding of jffs2 to look at it.
Also check other usage of jiffies - I found one more in
io/usb/eth/slave/current/host/ecos_usbeth.c
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^ permalink raw reply [flat|nested] 7+ messages in thread* [Bug 1001591] New: Bogus pseudo-randomness in garbage collect
@ 2012-05-21 13:02 bugzilla-daemon
2012-05-21 13:02 ` [Bug 1001591] Bogus pseudo-randomness in jffs2 " bugzilla-daemon
2012-05-26 15:46 ` bugzilla-daemon
0 siblings, 2 replies; 7+ messages in thread
From: bugzilla-daemon @ 2012-05-21 13:02 UTC (permalink / raw)
To: unassigned
Please do not reply to this email. Use the web interface provided at:
http://bugs.ecos.sourceware.org/show_bug.cgi?id=1001591
Summary: Bogus pseudo-randomness in garbage collect
Product: eCos
Version: CVS
Platform: All
OS/Version: All
Status: UNCONFIRMED
Severity: major
Priority: low
Component: Filesystem support
AssignedTo: unassigned@bugs.ecos.sourceware.org
ReportedBy: stano@meduna.org
CC: ecos-bugs@ecos.sourceware.org
Class: Advice Request
The jffs2_find_gc_block function in fs/jffs2/current/src/gc.c and
jffs2_mark_node_obsolete in nodemgmt.c try to do pseudo-random stuff by
computing jiffies % 128 and making probability decisions on the result. First I
think that this kind of pseudo-randomness is not really correct for embedded
systems that often have very predictable execution times.
But what is much worse, compat/linux/current/include/linux/kernel.h defines
jiffies as
#define jiffies 100
I am no expert at jffs2 and cannot say whether this can lead to major problems
or not, so I'd like someone with better understanding of jffs2 to look at it.
Also check other usage of jiffies - I found one more in
io/usb/eth/slave/current/host/ecos_usbeth.c
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^ permalink raw reply [flat|nested] 7+ messages in thread* [Bug 1001591] Bogus pseudo-randomness in jffs2 garbage collect
2012-05-21 13:02 [Bug 1001591] New: Bogus pseudo-randomness in " bugzilla-daemon
@ 2012-05-21 13:02 ` bugzilla-daemon
2012-05-26 15:46 ` bugzilla-daemon
1 sibling, 0 replies; 7+ messages in thread
From: bugzilla-daemon @ 2012-05-21 13:02 UTC (permalink / raw)
To: unassigned
Please do not reply to this email. Use the web interface provided at:
http://bugs.ecos.sourceware.org/show_bug.cgi?id=1001591
Stanislav Meduna <stano@meduna.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|Bogus pseudo-randomness in |Bogus pseudo-randomness in
|garbage collect |jffs2 garbage collect
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^ permalink raw reply [flat|nested] 7+ messages in thread* [Bug 1001591] Bogus pseudo-randomness in jffs2 garbage collect
2012-05-21 13:02 [Bug 1001591] New: Bogus pseudo-randomness in " bugzilla-daemon
2012-05-21 13:02 ` [Bug 1001591] Bogus pseudo-randomness in jffs2 " bugzilla-daemon
@ 2012-05-26 15:46 ` bugzilla-daemon
1 sibling, 0 replies; 7+ messages in thread
From: bugzilla-daemon @ 2012-05-26 15:46 UTC (permalink / raw)
To: unassigned
Please do not reply to this email. Use the web interface provided at:
http://bugs.ecos.sourceware.org/show_bug.cgi?id=1001591
Jonathan Larmour <jifl@ecoscentric.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jifl@ecoscentric.com
AssignedTo|unassigned@bugs.ecos.source |jifl@ecoscentric.com
|ware.org |
--- Comment #1 from Jonathan Larmour <jifl@ecoscentric.com> 2012-05-26 16:46:10 BST ---
(In reply to comment #0)
> The jffs2_find_gc_block function in fs/jffs2/current/src/gc.c and
> jffs2_mark_node_obsolete in nodemgmt.c try to do pseudo-random stuff by
> computing jiffies % 128 and making probability decisions on the result. First I
> think that this kind of pseudo-randomness is not really correct for embedded
> systems that often have very predictable execution times.
>
> But what is much worse, compat/linux/current/include/linux/kernel.h defines
> jiffies as
> #define jiffies 100
>
> I am no expert at jffs2 and cannot say whether this can lead to major problems
> or not, so I'd like someone with better understanding of jffs2 to look at it.
Yes. It's a problem but not a big one. It just means it loses an element of
pseudo-randomness which means that with certain repetitive usage patterns,
there may be uneven flash wear. I'll fix this to use cyg_current_time() which
is close enough to achieve the same job.
> Also check other usage of jiffies - I found one more in
> io/usb/eth/slave/current/host/ecos_usbeth.c
That file is genuinely for Linux so that's ok.
Jifl
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^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2012-05-27 0:53 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2012-05-21 13:02 [Bug 1001591] New: Bogus pseudo-randomness in garbage collect bugzilla-daemon
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2012-05-26 15:46 ` bugzilla-daemon
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2012-05-21 13:02 [Bug 1001591] New: Bogus pseudo-randomness in " bugzilla-daemon
2012-05-21 13:02 ` [Bug 1001591] Bogus pseudo-randomness in jffs2 " bugzilla-daemon
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