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42d3e2d041
virtiofs currently maps various buffers in scatter gather list and it looks at number of pages (ap->pages) and assumes that same number of pages will be used both for input and output (sg_count_fuse_req()), and calculates total number of scatterlist elements accordingly. But looks like this assumption is not valid in all the cases. For example, Cai Qian reported that trinity, triggers warning with virtiofs sometimes. A closer look revealed that if one calls ioctl(fd, 0x5a004000, buf), it will trigger following warning. WARN_ON(out_sgs + in_sgs != total_sgs) In this case, total_sgs = 8, out_sgs=4, in_sgs=3. Number of pages is 2 (ap->pages), but out_sgs are using both the pages but in_sgs are using only one page. In this case, fuse_do_ioctl() sets different size values for input and output. args->in_args[args->in_numargs - 1].size == 6656 args->out_args[args->out_numargs - 1].size == 4096 So current method of calculating how many scatter-gather list elements will be used is not accurate. Make calculations more precise by parsing size and ap->descs. Reported-by: Qian Cai <cai@redhat.com> Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Link: https://lore.kernel.org/linux-fsdevel/5ea77e9f6cb8c2db43b09fbd4158ab2d8c066a0a.camel@redhat.com/ Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
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.