The Linux kernel's blk-wbt subsystem had a vulnerability where wbt_init_enable_default() used WARN_ON_ONCE to report failures from wbt_alloc() and wbt_init(), which are expected failure paths under memory pressure or if writeback throttling is already registered. This caused unnecessary warnings and stack traces triggered by syzbot during memory allocation failures. The patch removes WARN_ON_ONCE, replacing it with simple if-checks and a pr_warn() to retain diagnostic information without causing disruptive warnings. This change prevents spurious warnings without affecting kernel functionality, as failure to initialize writeback throttling simply results in the disk operating without it, which is harmless.

This issue does not affect confidentiality or integrity and only impacts availability by potentially causing spurious kernel warnings and stack traces under certain conditions. The disk continues to operate normally without writeback throttling if initialization fails. There are no known exploits in the wild. The impact is limited to unnecessary kernel warnings that could confuse diagnostics or monitoring.

A fix is available that removes the WARN_ON_ONCE call and replaces it with conditional checks and a warning log without stack traces. Users should update to Linux kernel versions 7.0.0-28.28.1 or later where this fix is applied. No additional action is required as the failure paths are benign and do not affect system security or stability.