Date: Tue, 10 Nov 1998 16:56:26 +0200 (EET) From: Alexander Litvin <archer@lucky.net> To: Greg Lehey <grog@lemis.com> Cc: current@FreeBSD.ORG Subject: Re: The infamous dying daemons bug Message-ID: <199811101456.QAA28210@grape.carrier.kiev.ua> In-Reply-To: <199811092056.PAA22043@lor.watermarkgroup.com> <199811100136.DAA00563@grape.carrier.kiev.ua> <19981110154327.X499@freebie.lemis.com>
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In article <19981110154327.X499@freebie.lemis.com> you wrote:
GL> On Tuesday, 10 November 1998 at 3:36:28 +0200, Alexander Litvin wrote:
>> LC> I went through swap_pager.c today and found a problem that could potentially
>> LC> have bad consequences. It's a comparison between page index in the swap pager
>> LC> and the size of the vm object, since a shadowed object may have a non-zero
>> LC> paging offset with respect to the swap pager, the comparison should have taken
>> LC> the offset into account. This piece of code has been there since '95, so
>> LC> I can't say if this was responsible for the daemon dying problem.
>>
>> It is definitely not responsible. At least for this particular problem,
>> though it may fix something else ;)
>>
>> After applying the patch, and artificially exhausting memory, I promptly
>> got:
>>
>> Nov 10 03:15:34 grape /kernel: swap_pager: suggest more swap space: 61 MB
>> Nov 10 03:16:26 grape /kernel: pid 310 (sendmail), uid 0: exited on signal 11
>> Nov 10 03:17:26 grape /kernel: pid 311 (sendmail), uid 0: exited on signal 11
>> Nov 10 03:18:25 grape /kernel: pid 313 (sendmail), uid 0: exited on signal 11
>> Nov 10 03:19:25 grape /kernel: pid 353 (sendmail), uid 0: exited on signal 11
>> Nov 10 03:20:26 grape /kernel: pid 394 (sendmail), uid 0: exited on signal 11
GL> Ah, now that's one that I've been getting without exhausting memory.
GL> I'm assuming that these dying sendmails are children of the daemon.
GL> What happens when you kill -1 the daemon ("accepting connections on
GL> port 25 (sendmail)")? In my experience, it *always* dies with a
GL> SIGSEGV after these messages have occurred.
Well, as I understand, 'swap_pager: suggest more swap space' does
not mean that memory is exhausted, but only that it is about to
be exhausted. At least, in this case it didn't come to any processes
being killed by kernel.
You're right -- that sendmails were childs of a daemon (queue runners).
I'm not sure about what happens if I send SIGHUP to the daemon. I
think it may or may not restart -- it depends. Last time I examined
a 'deseased' daemon (it was not sendmail, but a dummy daemon written
specially for testing), it appeared that some range of process memory,
where code of dynamic library lives, was corrupt (zeroed in that case).
I'll try later to kill -1 such daemon. Now I'm in the process of testing
Dima's kludge. Until now I was unable to reproduce a problem. Daemons
keep living ;)
GL> Greg
GL> --
GL> See complete headers for address, home page and phone numbers
GL> finger grog@lemis.com for PGP public key
---
Dealing with failure is easy:
Work hard to improve.
Success is also easy to handle:
You've solved the wrong problem. Work hard to improve.
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