Re: CIFS improvements/wider testing needed

[VALETTE Eric RD-MAPS-REN <eric2.valette@francetelecom.com>]

Steve French wrote:
> Eric,
> Thanks for the feedback - any bugs which you report which I can
> reproduce - I will treat
> as a very high priority and your testing is helpful.

I know you have tried to reproduce them and failed. The question was how
to go further?

>> Trying to push Linux in corporate environments in such condition is
>> very difficult because, due to those bugs, you cannot:
>> 
>> 1) save a new openoffice document twice, 2) create mail folders
>> from inside thunderbird (local mailbox
> shared
>> with windows),
> 
> You can avoid these by mounting with "nobrl" (no remote byte range
> lock) mount option (smbfs does not send byte range locks so would not
> run into this problem, but would run into others). These appear to be
> byte range locking problems. The problem is that cifs has to map
> advisory to mandatory locks which only works if the application is
> reasonably well behaved (not even Samba has support for advisory
> locks although they will come with the new Unix extensions). It may
> be made worse by a bug in openoffice (some Linux apps such as
> Evolution lock on the "wrong" file handle which does not fail in
> posix, although is sloppy coding) but I have not confirmed the byte
> range lock sequence which openoffice is trying as we did with
> Evolution - I did confirm that nobrl (disabling the byte range locks
> on the client) works. Note that this mount option, although not
> listed as a bug fix in git per-se - was added to address the
> evolution etc. locking bugs. There are quite a few of the cifs
> changes that fall into that category.

Well I would be surprised the "cat >> titi" command does any of this
byte range lock. If the "create and later rewrite the same file"
sequence fails, with a simple cat command (cat > titi ... ^D; cat >>
titi), how can it works with complicated applications?


> 
>> 3) avoid to do FSCK after each reboot,
> Not sure that cifs would cause this unless you mean that cifs was
> hung and shutdown hung. 

Yes : the system hangs when shutting down as the result of the "umount
-a"  with the last message being as described in bug N° 3237. I have to
press power button for 5 seconds.

NB : manually doing the umount does exactly the same things.

> To avoid cases where cifs requests could stay
> blocked forever (especially locking requests), I added a umount_begin
> routine a few weeks ago to try to free threads blocked in cifs - but
> what I need from users/tests if they see a cifs umount fail is to 
> know where the requests are hung so I can add wakeup calls for that
> condition in cifs's umount_begin (you can do "echo t >
> /proc/sysrq-trigger" then "dmesg > debugdata" to get the debugdata
> which has the callstacks of processes blocked in kernel).

Will do that in the bug data.

>> <https://bugzilla.samba.org/show_bug.cgi?id=3237>

> Although I would like to find a workaround so it does not hang the 
> umount or fail umount I am not convinced that this is a typical
> regression - if a server sends an illegal response which we were not
> catching before ... it would be dangerous to call preventing that
> potential security problem a regression.

Hanging a system systematically leading to FSCK on each reboot is not
particularly helpfull given the fact that it happens whebn you are doing
a shutdown in most cases.


-- eric

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