On 3/12/2023 12:56, Alexandre Oliva wrote:
If two or more suitable entries with the same filename are found in __uc_fw_auto_select's fw_blobs, and that filename fails to load in the first attempt and in the retry, when __uc_fw_auto_select is called for the third time, the coincidence of strings will cause it to clear file_selected.path at the first hit, so it will return the second hit over and over again, indefinitely.
Of course this doesn't occur with the pristine blob lists, but a modified version could run into this, e.g., patching in a duplicate entry, or (as in our case) disarming blob loading by remapping their names to "/*(DEBLOBBED)*/", given a toolchain that unifies identical string literals.
Not sure what you mean by disarming?
I think what you are saying is that you made a change similar to this? #define __MAKE_UC_FW_PATH_MMP(prefix_, name_, major_, minor_, patch_) "i915/invalid_file_name.bin"
So all entries in the table have the exact same filename. And with the toolchain unification comment, that means not just a matching string but the same string pointer. Thus, the search code is getting confused.
I'm not sure that is really a valid use case that the driver code should be expected to support. I'm not even sure what the purpose of your testing is? Even without the infinite loop, the driver is not going to load because you have removed the firmware files?
However, I think you are saying that the problem would also exist if there was some kind of genuine duplication in the table? Can you give an example of a genuine use case problem? If the same string is used for different platforms, I believe that should be fine. E.g. there are already a bunch of different platforms that all use the same TGL firmware file. Even with the string unification, that should not be an issue because the search is within a platform only. So there can only be a problem if a single platform specifies the same filename multiple times? Which would be a bug in the table because why? It would be redundant entries that have no purpose.
Note that I'm not saying we don't want to take your change. But I would like to understand if there is a genuine issue that maybe needs a better fix. E.g. should the table verification code be enhanced to just reject the table entirely if there are such errors present.
Also, is this string unification thing a part of the current gcc toolchain? Or are you saying that is a new feature that is not generally available yet? Or maybe only exists in some non-gcc toolchain?
Thanks, John.
Of course I'm ready to carry a patchlet to avoid this problem triggered by our (GNU Linux-libre's) intentional changes, but I figured you might be interested in fail-safing it even in accidental backporting circumstances. I realize it's not entirely foolproof: if the same string appears in two entries separated by a different one, the infinite loop might still occur. Catching that even more unlikely situation seemed too expensive.
Link: https://www.fsfla.org/pipermail/linux-libre/2023-March/003506.html Cc: intel-gfx@lists.freedesktop.org Cc: stable@vger.kernel.org # 6.[12].x Signed-off-by: Alexandre Oliva lxoliva@fsfla.org
drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c index 9d6f571097e6..2b7564a3ed82 100644 --- a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c @@ -259,7 +259,10 @@ __uc_fw_auto_select(struct drm_i915_private *i915, struct intel_uc_fw *uc_fw) uc_fw->file_selected.path = NULL; continue;
}
} else if (uc_fw->file_wanted.path == blob->path)/* Avoid retrying forever when neighborentries point to the same path. */continue;uc_fw->file_selected.path = blob->path; uc_fw->file_wanted.path = blob->path;