Messages in this thread Patch in this message | | | Date | Tue, 6 Oct 2009 22:03:40 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: [PATCH] swapfile: avoid NULL pointer dereference in swapon when s_bdev is NULL |
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On Thu, 1 Oct 2009, Suresh Jayaraman wrote: > Hugh Dickins wrote: > > On Thu, 1 Oct 2009, Suresh Jayaraman wrote: > >> > >> The call sequence is add_to_swap() -> get_swap_page() -> scan_swap_map() > >> -> discard_swap_cluster() -> blkdev_issue_discard(). > >> > >> Wrapping the code around a NULL check fixes the Oops for me. > > > > That's odd: scan_swap_map() should only discard_swap_cluster() if > > SWP_DISCARDABLE got set, and your first patch made sure that it wasn't. > > I forgot to mention, this is not on loopback NFS mount but an remote NFS > mount (so possibly s_bdev is not NULL) when doing swapon. The oops was > triggered when memhog program tries to use the swap space on the newly > created swapfile on NFS. I have not completely investigated the issue, > perhaps s_bdev is not being set when it ought to be..
I'm happy to see your first patch already in 2.6.32-rc3, but still suspicious of this second patch you sent afterwards. A quick skim through your patchset suggests 23/31 is probably responsible:
--- mmotm.orig/include/linux/swap.h +++ mmotm/include/linux/swap.h @@ -120,6 +120,7 @@ struct swap_extent { enum { SWP_USED = (1 << 0), /* is slot in swap_info[] used? */ SWP_WRITEOK = (1 << 1), /* ok to write to this swap? */ + SWP_FILE = (1 << 2), /* file swap area */ SWP_DISCARDABLE = (1 << 2), /* blkdev supports discard */ SWP_DISCARDING = (1 << 3), /* now discarding a free cluster */ SWP_SOLIDSTATE = (1 << 4), /* blkdev seeks are cheap */ Hugh
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