6.6-stable review patch. If anyone has any objections, please let me know.
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From: Nathan Chancellor nathan@kernel.org
[ Upstream commit aaf043a5688114703ae2c1482b92e7e0754d684e ]
When building with Clang 20 or newer, there are some objtool warnings from unexpected fallthroughs to other functions:
vmlinux.o: warning: objtool: mlx5e_mpwrq_mtts_per_wqe() falls through to next function mlx5e_mpwrq_max_num_entries() vmlinux.o: warning: objtool: mlx5e_mpwrq_max_log_rq_size() falls through to next function mlx5e_get_linear_rq_headroom()
LLVM 20 contains an (admittedly problematic [1]) optimization [2] to convert divide by zero into the equivalent of __builtin_unreachable(), which invokes undefined behavior and destroys code generation when it is encountered in a control flow graph.
mlx5e_mpwrq_umr_entry_size() returns 0 in the default case of an unrecognized mlx5e_mpwrq_umr_mode value. mlx5e_mpwrq_mtts_per_wqe(), which is inlined into mlx5e_mpwrq_max_log_rq_size(), uses the result of mlx5e_mpwrq_umr_entry_size() in a divide operation without checking for zero, so LLVM is able to infer there will be a divide by zero in this case and invokes undefined behavior. While there is some proposed work to isolate this undefined behavior and avoid the destructive code generation that results in these objtool warnings, code should still be defensive against divide by zero.
As the WARN_ONCE() implies that an invalid value should be handled gracefully, return 1 instead of 0 in the default case so that the results of this division operation is always valid.
Fixes: 168723c1f8d6 ("net/mlx5e: xsk: Use umr_mode to calculate striding RQ parameters") Link: https://lore.kernel.org/CAGG=3QUk8-Ak7YKnRziO4=0z=1C_7+4jF+6ZeDQ9yF+kuTOHOQ@... [1] Link: https://github.com/llvm/llvm-project/commit/37932643abab699e8bb1def08b7eb4ea... [2] Closes: https://github.com/ClangBuiltLinux/linux/issues/2131 Closes: https://github.com/ClangBuiltLinux/linux/issues/2132 Signed-off-by: Nathan Chancellor nathan@kernel.org Reviewed-by: Tariq Toukan tariqt@nvidia.com Link: https://patch.msgid.link/20251014-mlx5e-avoid-zero-div-from-mlx5e_mpwrq_umr_... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/ethernet/mellanox/mlx5/core/en/params.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c index dcd5db907f102..9c22d64af6853 100644 --- a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c @@ -98,7 +98,7 @@ u8 mlx5e_mpwrq_umr_entry_size(enum mlx5e_mpwrq_umr_mode mode) return sizeof(struct mlx5_ksm) * 4; } WARN_ONCE(1, "MPWRQ UMR mode %d is not known\n", mode); - return 0; + return 1; }
u8 mlx5e_mpwrq_log_wqe_sz(struct mlx5_core_dev *mdev, u8 page_shift,