Currently we allocate rx buffers in a single contiguous buffers for
headers (iser and iscsi) and data trailer. This means that most likely
the data starting offset is aligned to 76 bytes (size of both headers).
This worked fine for years, but at some point this broke, resulting in
data corruptions in isert when a command comes with immediate data
and the underlying backend device assumes 512 bytes buffer alignment.
We assume a hard-requirement for all direct I/O buffers to be 512 bytes
aligned. To fix this, we should avoid passing unaligned buffers for I/O.
Instead, we allocate our recv buffers with some extra space such that we
can have the data portion align to 512 byte boundary. This also means
that we cannot reference headers or data using structure but rather
accessors (as they may move based on alignment). Also, get rid of the
wrong __packed annotation from iser_rx_desc as this has only harmful
effects (not aligned to anything).
This affects the rx descriptors for iscsi login and data plane.
Reported-by: Stephen Rust <srust@xxxxxxxxxxxxxxx>
Tested-by: Doug Dumitru <doug@xxxxxxxxxxx>
Signed-off-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
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Changes from v1:
- revised change log
This still needs to identify when this regression occurred for
backporting, what is the fixes line?
I don't have the exact bisection, the original report mentioned:
3d75ca0adef4 ("block: introduce multi-page bvec helpers")
But I cannot explain what in that patch caused this.
