* Re: is flock broken in 2.4 or 2.5 kernels or what does this mean?
2002-07-23 16:31 ` Alan Cox
@ 2002-07-23 15:27 ` Richard A Nelson
2002-07-23 15:50 ` Jirka Kosina
` (2 subsequent siblings)
3 siblings, 0 replies; 10+ messages in thread
From: Richard A Nelson @ 2002-07-23 15:27 UTC (permalink / raw)
To: Alan Cox; +Cc: John Covici, linux-kernel
On 23 Jul 2002, Alan Cox wrote:
> Date: 23 Jul 2002 17:31:12 +0100
> From: Alan Cox <alan@lxorguk.ukuu.org.uk>
> To: John Covici <covici@ccs.covici.com>
> Cc: linux-kernel@vger.kernel.org
> Subject: Re: is flock broken in 2.4 or 2.5 kernels or what does this mean?
>
> On Tue, 2002-07-23 at 15:41, John Covici wrote:
> > In the latest release notes of sendmail I have read the following:
> >
> > NOTE: Linux appears to have broken flock() again. Unless
> > the bug is fixed before sendmail 8.13 is shipped,
> > 8.13 will change the default locking method to
> > fcntl() for Linux kernel 2.4 and later. You may
> > want to do this in 8.12 by compiling with
> > -DHASFLOCK=0. Be sure to update other sendmail
> > related programs to match locking techniques.
> >
> > Can anyone tell me what this is all about -- is there any basis in
> > reality for what they are saying?
>
> First I've heard of it, so it would be useful if someone has access to
> the sendmail problem report/test in question that shows it and I'll go
> find out.
Indeed it is, this message explains it fairly well:
Message-ID: <20020702160118.C4711@redhat.com>
Date: Tue, 2 Jul 2002 16:01:18 +0100
From: Stephen C. Tweedie <sct@redhat.com>
I haven't heard of any plans to incorporate the removal of accounting
info in either 2.4 or 2.5 ;(
--
Rick Nelson
Your job is being a professor and researcher: That's one hell of a good excuse
for some of the brain-damages of minix.
(Linus Torvalds to Andrew Tanenbaum)
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: is flock broken in 2.4 or 2.5 kernels or what does this mean?
2002-07-23 16:31 ` Alan Cox
2002-07-23 15:27 ` Richard A Nelson
@ 2002-07-23 15:50 ` Jirka Kosina
2002-07-23 21:44 ` J.A. Magallon
2002-07-23 23:20 ` Andrea Arcangeli
3 siblings, 0 replies; 10+ messages in thread
From: Jirka Kosina @ 2002-07-23 15:50 UTC (permalink / raw)
To: Alan Cox; +Cc: John Covici, linux-kernel
On 23 Jul 2002, Alan Cox wrote:
> > Can anyone tell me what this is all about -- is there any basis in
> > reality for what they are saying?
> First I've heard of it, so it would be useful if someone has access to
> the sendmail problem report/test in question that shows it and I'll go
> find out.
Quoting Stephen Tweedie's earlier post to the list:
==
It really is broken, and sendmail triggers it (at least their
commercial binaries do). I've already been talking to willy about the
problem. The trouble is the accounting: if one process opens a fd and then
fork()s, it is possible for the lock to be taken in the parent and
released in the child (or vice versa) --- unless there's an explicit
flock(LOCK_UN), then the lock will be released implicitly when the
last reference to the fd is closed. When this happens, we get the lock
count incremented in one task and
decremented in another. That can wrap the lock count backwards to -1
(or rather ~0UL), which causes the locks rlimit check to think we've
exceeded the lock quota and new lock requests will fail. It's easy to
reproduce this: try the attached prog. It produces an erroneous
ENOLCK due to the bug.
==
--
JiKos.
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: is flock broken in 2.4 or 2.5 kernels or what does this mean?
2002-07-23 16:31 ` Alan Cox
2002-07-23 15:27 ` Richard A Nelson
2002-07-23 15:50 ` Jirka Kosina
@ 2002-07-23 21:44 ` J.A. Magallon
2002-07-24 16:08 ` David Ford
2002-07-23 23:20 ` Andrea Arcangeli
3 siblings, 1 reply; 10+ messages in thread
From: J.A. Magallon @ 2002-07-23 21:44 UTC (permalink / raw)
To: Alan Cox; +Cc: John Covici, linux-kernel
On 2002.07.23 Alan Cox wrote:
>On Tue, 2002-07-23 at 15:41, John Covici wrote:
>> In the latest release notes of sendmail I have read the following:
>>
>> NOTE: Linux appears to have broken flock() again. Unless
>> the bug is fixed before sendmail 8.13 is shipped,
>> 8.13 will change the default locking method to
>> fcntl() for Linux kernel 2.4 and later. You may
>> want to do this in 8.12 by compiling with
>> -DHASFLOCK=0. Be sure to update other sendmail
>> related programs to match locking techniques.
>>
>> Can anyone tell me what this is all about -- is there any basis in
>> reality for what they are saying?
>
>First I've heard of it, so it would be useful if someone has access to
>the sendmail problem report/test in question that shows it and I'll go
>find out.
>
Perhaps if you have your spool over nfs:
man flock:
NOTES
flock(2) does not lock files over NFS. Use fcntl(2)
instead: that does work over NFS, given a sufficiently
recent version of Linux and a server which supports lock
ing.
flock(2) and fcntl(2) locks have different semantics with
respect to forked processes and dup(2).
--
J.A. Magallon \ Software is like sex: It's better when it's free
mailto:jamagallon@able.es \ -- Linus Torvalds, FSF T-shirt
Linux werewolf 2.4.19-rc3-jam1, Mandrake Linux 9.0 (Cooker) for i586
gcc (GCC) 3.1.1 (Mandrake Linux 8.3 3.1.1-0.10mdk)
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: is flock broken in 2.4 or 2.5 kernels or what does this mean?
2002-07-23 21:44 ` J.A. Magallon
@ 2002-07-24 16:08 ` David Ford
2002-07-25 1:28 ` Alan Cox
0 siblings, 1 reply; 10+ messages in thread
From: David Ford @ 2002-07-24 16:08 UTC (permalink / raw)
To: J.A. Magallon; +Cc: Alan Cox, John Covici, linux-kernel
(Alan)
Actually I posted a "is sendmail on crack?" question last month when
8.12.5 was released and this was in the release notes. We got a bunch
of confirmations that Linux flock() was broken due to the accounting.
David
J.A. Magallon wrote:
>On 2002.07.23 Alan Cox wrote:
>
>
>>On Tue, 2002-07-23 at 15:41, John Covici wrote:
>>
>>
>>>In the latest release notes of sendmail I have read the following:
>>>
>>> NOTE: Linux appears to have broken flock() again. Unless
>>> the bug is fixed before sendmail 8.13 is shipped,
>>> 8.13 will change the default locking method to
>>> fcntl() for Linux kernel 2.4 and later. You may
>>> want to do this in 8.12 by compiling with
>>> -DHASFLOCK=0. Be sure to update other sendmail
>>> related programs to match locking techniques.
>>>
>>>Can anyone tell me what this is all about -- is there any basis in
>>>reality for what they are saying?
>>>
>>>
>>First I've heard of it, so it would be useful if someone has access to
>>the sendmail problem report/test in question that shows it and I'll go
>>find out.
>>
>>
>>
>
>Perhaps if you have your spool over nfs:
>
>man flock:
>
>NOTES
> flock(2) does not lock files over NFS. Use fcntl(2)
> instead: that does work over NFS, given a sufficiently
> recent version of Linux and a server which supports lock
> ing.
>
> flock(2) and fcntl(2) locks have different semantics with
> respect to forked processes and dup(2).
>
>
>
--
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^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: is flock broken in 2.4 or 2.5 kernels or what does this mean?
2002-07-24 16:08 ` David Ford
@ 2002-07-25 1:28 ` Alan Cox
0 siblings, 0 replies; 10+ messages in thread
From: Alan Cox @ 2002-07-25 1:28 UTC (permalink / raw)
To: David Ford; +Cc: J.A. Magallon, John Covici, linux-kernel
On Wed, 2002-07-24 at 17:08, David Ford wrote:
> (Alan)
> Actually I posted a "is sendmail on crack?" question last month when
> 8.12.5 was released and this was in the release notes. We got a bunch
> of confirmations that Linux flock() was broken due to the accounting.
Thanks. I now have the original discussion, the demonstration and a
patch Andrea believes fixes it.
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: is flock broken in 2.4 or 2.5 kernels or what does this mean?
2002-07-23 16:31 ` Alan Cox
` (2 preceding siblings ...)
2002-07-23 21:44 ` J.A. Magallon
@ 2002-07-23 23:20 ` Andrea Arcangeli
3 siblings, 0 replies; 10+ messages in thread
From: Andrea Arcangeli @ 2002-07-23 23:20 UTC (permalink / raw)
To: Alan Cox; +Cc: John Covici, linux-kernel
On Tue, Jul 23, 2002 at 05:31:12PM +0100, Alan Cox wrote:
> On Tue, 2002-07-23 at 15:41, John Covici wrote:
> > In the latest release notes of sendmail I have read the following:
> >
> > NOTE: Linux appears to have broken flock() again. Unless
> > the bug is fixed before sendmail 8.13 is shipped,
> > 8.13 will change the default locking method to
> > fcntl() for Linux kernel 2.4 and later. You may
> > want to do this in 8.12 by compiling with
> > -DHASFLOCK=0. Be sure to update other sendmail
> > related programs to match locking techniques.
> >
> > Can anyone tell me what this is all about -- is there any basis in
> > reality for what they are saying?
>
> First I've heard of it, so it would be useful if someone has access to
> the sendmail problem report/test in question that shows it and I'll go
> find out.
fix is in -aa from Matthew Wilcox:
http://www.us.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.19rc3aa1/00_drop-broken-flock-account-1
fcntl API never obeyed to the accounting anyways.
Andrea
^ permalink raw reply [flat|nested] 10+ messages in thread