Messages in this thread Patch in this message |  | | | From | "Stephen C. Tweedie" <> | | Date | Fri, 23 Apr 1999 14:25:28 +0100 (BST) | | Subject | Re: RFC: patch for suspected shm swap problem |
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Hi,
On Thu, 22 Apr 1999 09:03:14 -0700 (PDT), kanoj@google.engr.sgi.com (Kanoj Sarcar) said:
> I suspect the problem is that shm_swap bumps up swap_id to more > than max_shmid under some circumstances, leading the next call > to shm_swap to trip. Note that valid values of max_shmid are 0 .. > SHMMNI - 1, but shm_swap can leave swap_id set to SHMMNI.
> MMU code maintainers, could you please review the patch and let > me know whether it is good
Agreed: the patch looks correct.
In particular, with the patch in place we are still protected against having max_shmid shrink between calls to shm_swap(): the worst that can happen is that we find an unused shm_seg which will get caught by the IPC_UNUSED test near the top of shm_swap. Only if the shm table is full, and so the swap_id overflow forces the next shm_segs[swap_id] to point to an entry not preinitialised to IPC_UNUSED or IPC_NOID, will there be a danger, and the patch makes sure that we never overstep that bound. (This probably explains why we haven't seen the problem before: were you allocating the maximum number of shm segments during the stress test?)
--Stephen
---------------------------------------------------------------- From: kanoj@google.engr.sgi.com (Kanoj Sarcar) Sender: owner-linux-kernel@vger.rutgers.edu To: Linux-MM@kvack.org, linux-kernel@vger.rutgers.edu Subject: RFC: patch for suspected shm swap problem Date: Thu, 22 Apr 1999 09:03:14 -0700 (PDT) Hi,
While running some heavy stress on shm code, I took a panic in shm_swap coming out of do_try_to_free_pages in the context of non-kswapd processes. From the register display, I suspect the problem to be fixed by this patch:
--- /usr/tmp/p_rdiff_a000PE/shm.c Tue Apr 20 16:07:02 1999 +++ kern/ipc/shm.c Tue Apr 20 16:05:54 1999 @@ -716,10 +716,10 @@ next_id: swap_idx = 0; if (++swap_id > max_shmid) { + swap_id = 0; if (loop) goto failed; loop = 1; - swap_id = 0; } goto check_id; } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/
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