f9bd84a8a8
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") Reviewed-by: David Woodhouse <dwmw@amazon.de> Reviewed-by: Maximilian Heyne <mheyne@amazon.de> Reviewed-by: Paul Durrant <pdurrant@amazon.co.uk> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com> Signed-off-by: SeongJae Park <sjpark@amazon.de> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.