On 27.11.19 10:13, Roger Pau Monné wrote: > On Tue, Nov 26, 2019 at 04:36:05PM +0100, SeongJae Park wrote: >> From: SeongJae Park <sjp...@amazon.de> >> >> 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 <sjp...@amazon.de> >> Reviewed-by: David Woodhouse <d...@amazon.de> >> Reviewed-by: Maximilian Heyne <mhe...@amazon.de> >> Reviewed-by: Paul Durrant <pdurr...@amazon.co.uk> > Reviewed-by: Roger Pau Monné <roger....@citrix.com> > > Thanks, Roger.
May I ask some more comments? Thanks, SeongJae Park _______________________________________________ Xen-devel mailing list Xenfirstname.lastname@example.org https://lists.xenproject.org/mailman/listinfo/xen-devel