On Tue, Nov 26, 2019 at 04:36:05PM +0100, SeongJae Park wrote: > From: SeongJae Park <[email protected]> > > For each I/O request, blkback first maps the foreign pages for the > request to its local pages. If an allocation of a local page for the > mapping fails, it should unmap every mapping already made for the > request. > > However, blkback's handling mechanism for the allocation failure does > not mark the remaining foreign pages as unmapped. Therefore, the unmap > function merely tries to unmap every valid grant page for the request, > including the pages not mapped due to the allocation failure. On a > system that fails the allocation frequently, this problem leads to > following kernel crash. > > [ 372.012538] BUG: unable to handle kernel NULL pointer dereference at > 0000000000000001 > [ 372.012546] IP: [<ffffffff814071ac>] gnttab_unmap_refs.part.7+0x1c/0x40 > [ 372.012557] PGD 16f3e9067 PUD 16426e067 PMD 0 > [ 372.012562] Oops: 0002 [#1] SMP > [ 372.012566] Modules linked in: act_police sch_ingress cls_u32 > ... > [ 372.012746] Call Trace: > [ 372.012752] [<ffffffff81407204>] gnttab_unmap_refs+0x34/0x40 > [ 372.012759] [<ffffffffa0335ae3>] xen_blkbk_unmap+0x83/0x150 > [xen_blkback] > ... > [ 372.012802] [<ffffffffa0336c50>] dispatch_rw_block_io+0x970/0x980 > [xen_blkback] > ... > Decompressing Linux... Parsing ELF... done. > Booting the kernel. > [ 0.000000] Initializing cgroup subsys cpuset > > This commit fixes this problem by marking the grant pages of the given > request that didn't mapped due to the allocation failure as invalid. > > Fixes: c6cc142dac52 ("xen-blkback: use balloon pages for all mappings") > > Signed-off-by: SeongJae Park <[email protected]> > Reviewed-by: David Woodhouse <[email protected]> > Reviewed-by: Maximilian Heyne <[email protected]> > Reviewed-by: Paul Durrant <[email protected]>
Reviewed-by: Roger Pau Monné <[email protected]> Thanks, Roger. _______________________________________________ Xen-devel mailing list [email protected] https://lists.xenproject.org/mailman/listinfo/xen-devel
