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Message-ID: <b94f08a6-a2e2-c719-37ac-7c412fe1b519@colorfullife.com>
Date:   Sun, 4 Sep 2022 19:38:30 +0200
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Subject: Re: Request to cherry-pick 20401d1058f3f841f35a594ac2fc1293710e55b9
 to v5.10 and v5.4
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Varsha Teratipally <teratipally@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Davidlohr Bueso <dbueso@suse.de>,
        Rafael Aquini <aquini@redhat.com>,
        Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
References: <20220902135912.816188-1-teratipally@google.com>
 <YxIS4jWE03E5pZjS@kroah.com>
Content-Language: en-US
From:   Manfred Spraul <manfred@colorfullife.com>
In-Reply-To: <YxIS4jWE03E5pZjS@kroah.com>
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Hi,

On 9/2/22 16:27, Greg Kroah-Hartman wrote:
> On Fri, Sep 02, 2022 at 01:59:11PM +0000, Varsha Teratipally wrote:
>> Hi all,
>>
>> Commit 20401d1058f3f841f35a594ac2fc1293710e55b9("ipc: replace costly
>> bailout check in sysvipc_find_ipc()" fixes a high cve and optimizes the
>> costly loop by adding a checkpoint, which I think might be a good
>> candidate for the stable branches
> What do you mean by "high cve"?
>
> And that feels like it's an artificial benchmark fixup, what real
> workload benefits from this change?

Standard ipcs end up parsing /proc/sysvipc/*, thus there are real users 
where the performance of /proc/sysvsem/* matters.

But:

The performance of the function was bad since 2007, i.e. why is is now 
urgent? I do not see a bug that must be fixed.

Initial patch:

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/ipc/util.c?id=7ca7e564e049d8b350ec9d958ff25eaa24226352

(core issue: The code needs to find the next entry in an idr. And 
instead of using idr_get_next(), it uses idr_find() in a for(;;id++) loop.)

<<<

[manfred@localhost Input]$ rpm -qf /usr/bin/ipcs
util-linux-core-2.38-1.fc36.x86_64


[manfred@localhost Input]$ strace -e openat /usr/bin/ipcs
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/lib/locale/en_US.UTF-8/LC_TIME", 
O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/locale/en_US.utf8/LC_TIME", 
O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/lib64/gconv/gconv-modules.cache", O_RDONLY) = 3

openat(AT_FDCWD, 
"/usr/share/locale/en_US.UTF-8/LC_MESSAGES/util-linux.mo", O_RDONLY) = 
-1 ENOENT (No such file or directory)
openat(AT_FDCWD, 
"/usr/share/locale/en_US.utf8/LC_MESSAGES/util-linux.mo", O_RDONLY) = -1 
ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en_US/LC_MESSAGES/util-linux.mo", 
O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en.UTF-8/LC_MESSAGES/util-linux.mo", 
O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en.utf8/LC_MESSAGES/util-linux.mo", 
O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en/LC_MESSAGES/util-linux.mo", 
O_RDONLY) = -1 ENOENT (No such file or directory)
------ Message Queues --------
key        msqid      owner      perms      used-bytes messages
openat(AT_FDCWD, "/proc/sysvipc/msg", O_RDONLY) = 3

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch status
openat(AT_FDCWD, "/proc/sysvipc/shm", O_RDONLY) = 3
openat(AT_FDCWD, "/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
0x00000000 18         manfred    600        524288     2 dest
openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
0x5125004a 19         manfred    600        3208 1

------ Semaphore Arrays --------
key        semid      owner      perms      nsems
openat(AT_FDCWD, "/proc/sysvipc/sem", O_RDONLY) = 3
openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
0x51250047 0          manfred    600        1
openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
0x51250049 2          manfred    600        1

 >>>