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Date:   Tue, 05 May 2020 18:13:08 +0200
From:   Andreas Schwab <schwab@...e.de>
To:     Vasily Averin <vvs@...tuozzo.com>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        NeilBrown <neilb@...e.com>, Waiman Long <longman@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>
Subject: Re: [PATCH 7/7] sysvipc_find_ipc should increase position index

I think this is causing this bug (seen on 5.6.8):

# ipcs -q

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    

# ipcmk -Q
Message queue id: 0
# ipcs -q

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    
0x82db8127 0          root       644        0            0           

# ipcmk -Q
Message queue id: 1
# ipcs -q

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    
0x82db8127 0          root       644        0            0           
0x76d1fb2a 1          root       644        0            0           

# ipcrm -q 0
# ipcs -q

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    
0x76d1fb2a 1          root       644        0            0           
0x76d1fb2a 1          root       644        0            0           

# ipcmk -Q
Message queue id: 2
# ipcrm -q 2
# ipcs -q

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    
0x76d1fb2a 1          root       644        0            0           
0x76d1fb2a 1          root       644        0            0           

# ipcmk -Q
Message queue id: 3
# ipcrm -q 1
# ipcs -q

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    
0x7c982867 3          root       644        0            0           
0x7c982867 3          root       644        0            0           
0x7c982867 3          root       644        0            0           
0x7c982867 3          root       644        0            0           


As you can see, whenever an IPC item with a low id is deleted, the items
with higher ids are duplicated, as if filling a hole.

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@...e.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

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