| commit | 1900e9dd11ab1c621242faedb14afa96a59e4608 | [log] [tgz] |
|---|---|---|
| author | Adrian Danis <adanis@google.com> | Thu Jul 09 00:50:23 2020 +0000 |
| committer | CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org> | Thu Jul 09 00:50:23 2020 +0000 |
| tree | c5b67a5835f709c217dd728dd397d04925805160 | |
| parent | cac51529ef67d855eb9398c1a287794c9a0c6602 [diff] |
[kernel][vm] Forbid zero length pins Pinning a zero length range results in potentially inconsistent semantics compared with non zero sized pin. For example, a non-zero length pin will prevent a VMO from being resized smaller than the pin offset. Whereas a zero length pin does not prevent this. This might be okay, but then attemping to Unpin that zero length range can fail, as it is outside the VMO. Instead of forbidding zero length pins, unpin could instead be changed to always consider a zero length unpin to be success. This is only partially correct though, as we really should only consider a zero length unpin to be correct if there was an equivalent zero length pin. Unfortunately tracking this would require additional metadata to be allocated. This issue, and the fact that it still leaves the inconsistent resize semantics is why this option was not taken. In the autocall cleanup of CommitRangeInternal any pinned portion is automatically unpinned. Previously this would just always call Unpin, even if the range to Unpin was zero. The range could be zero if the VMO was resized before the first page was pinned. This can only happen in the case of a user pager backed VMO where the resize happens whilst blocked waiting for the page to populate. The current user facing API already forbids zero length pin requests, so this change is not visible outside of some existing in kernel unittests that were updated. Bug: 53711 Change-Id: Iabf5022bdd2404e25a3253871be90328982dc9d1 Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/404534 Commit-Queue: Adrian Danis <adanis@google.com> Reviewed-by: Rasha Eqbal <rashaeqbal@google.com> Reviewed-by: Nick Maniscalco <maniscalco@google.com> Testability-Review: Rasha Eqbal <rashaeqbal@google.com> Testability-Review: Nick Maniscalco <maniscalco@google.com>
Pink + Purple == Fuchsia (a new operating system)
Fuchsia is a modular, capability-based operating system. Fuchsia runs on modern 64-bit Intel and ARM processors.
Fuchsia is an open source project with a code of conduct that we expect everyone who interacts with the project to respect.
See Getting Started.
See fuchsia.dev.