linux-kernel - RE: BUG REPORT - IDR wraps around at 30-bits

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Message-ID: <199217e8a2fc33f6aa0ecf764a0104cb@mail.gmail.com>
Date:	Tue, 13 Aug 2013 12:51:14 +0530
From:	Shyam Kaushik <shyam@...arastorage.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: RE: BUG REPORT - IDR wraps around at 30-bits - works very bad with NFSD/SCTP

Hi Greg,

Unfortunately we dont have a 3.9/3.10 environment here. So if IDR
developers can try the example code, it should show if the bug is still
present in there. Thanks.

--Shyam

-----Original Message-----
From: Greg KH [mailto:gregkh@...uxfoundation.org]
Sent: Tuesday, August 13, 2013 12:50 PM
To: Shyam Kaushik
Cc: Tejun Heo; Andrew Morton; linux-kernel@...r.kernel.org
Subject: Re: BUG REPORT - IDR wraps around at 30-bits - works very bad
with NFSD/SCTP

On Tue, Aug 13, 2013 at 12:31:29PM +0530, Shyam Kaushik wrote:
> Hi Folks,
>
> We are using Ubuntu linux kernel 3.2.0-25-generic &
3.8.13-030813-generic
> in our environments, but I think this bug is still present in mainline
> kernel. Clients of IDR rollover at MAX_INT (NFSD & SCTP in kernel do
this)
> & others on MAX_IDR_MASK. This is ideally 2^31. But there is some BUG
> within IDR that it wraps over at 2^30.
>
> NFSD uses IDR for maintaining its stateids & tracks min_stateid with a
> static variable which keeps incrementing. So over a period of time NFSD
> could run into the issue that it allocates an ID with IDR, but IDR cant
> locate this ID, resulting in NFSD constantly sending BAD_STATEIDS to all
> its clients.
>
> Following short driver (which closely resembles NFSD usage of IDR) shows
> the BUG within IDR:

The IDR code was rewritten very recently (3.9 or 3.10), so could you
test 3.10.6 out and let us know if this is still an issue there?  And if
so, cc: the idr developers (on cc:) would help out a lot.

Example left below for them...

thanks,

greg k-h

>
> #include <linux/module.h>
> #include <linux/init.h>
> #include <linux/version.h>
> #include <linux/idr.h>
>
> static int log_idr_entry(int id, void *ptr, void *data)
> {
>         int     *expected_val = (int *)ptr;
>
>         pr_info("\tIDR Actual ID[%d] %s Expected Value[%d]\n", id, (id
==
> *expected_val)?"==":"!=", *expected_val);
>         return 0;
> }
>
> static void process_idr_entry(struct idr *stateids, int min_stateid)
> {
>         int             new_stid;
>         int             error;
>
>         pr_info("\nProcessing for min_stateid[%d]\n", min_stateid);
>         if (!idr_pre_get(stateids, GFP_KERNEL)) {
>                 pr_info("Failed to pre-get\n");
>                 return;
>         }
>
>         error = idr_get_new_above(stateids, &new_stid, min_stateid,
> &new_stid);
>         if (error) {
>                 pr_info("Failed to get new id\n");
>                 idr_remove(stateids, new_stid);
>                 return;
>         }
>
>         pr_info("Allocated new_stid[%d]\n", new_stid);
>
>         if (!idr_find(stateids, new_stid))
>                 pr_info("BUG: Cant find ID[%d]\n", new_stid);
>
>         pr_info("Dumping entries in IDR\n");
>         idr_for_each(stateids, &log_idr_entry, NULL);
>         idr_remove(stateids, new_stid);
> }
>
> void driver_exit(void)
> {
> }
>
> int driver_init(void)
> {
>         struct idr      stateids;
>
>         pr_info("%d\n", MAX_INT);
>         idr_init(&stateids);
>         process_idr_entry(&stateids, 0/*min_stateid*/);
>         process_idr_entry(&stateids, 1073741823/*min_stateid*/);
>         process_idr_entry(&stateids, 1073741824/*min_stateid*/);
>         idr_remove_all(&stateids);
>         idr_destroy(&stateids);
>         return 0;
> }
>
> module_init(driver_init);
> module_exit(driver_exit);
>
>
> Upon loading the driver, the following message shows up
> [71641.440846] Processing for min_stateid[0]
> [71641.440857] Allocated new_stid[0]
> [71641.440859] Dumping entries in IDR
> [71641.440861]  IDR Actual ID[0] == Expected Value[0]
> [71641.440864]
> [71641.440864] Processing for min_stateid[1073741823]
> [71641.440867] Allocated new_stid[1073741823]
> [71641.440868] Dumping entries in IDR
> [71641.440876]  IDR Actual ID[1073741823] == Expected Value[1073741823]
> [71641.440878]
> [71641.440878] Processing for min_stateid[1073741824]
> [71641.440883] Allocated new_stid[1073741824]
> [71641.440884] BUG: Cant find ID[1073741824]
> [71641.440886] Dumping entries in IDR
> [71641.440887]  IDR Actual ID[0] != Expected Value[1073741824]
>
> i.e. when we allocate a stated==1073741824, IDR internally has it as 0.
>
> --Shyam
> --
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