CVE-2022-49540: 
Linux Kernel vulnerability analysis and mitigation

In the Linux kernel, CVE-2022-49540 addresses a race condition vulnerability in the RCU (Read-Copy-Update) tasks subsystem. The issue occurs during the booting of secondary CPUs, where cpusread[lock/unlock] fails to maintain a stable online CPU mask, resulting in potential system instability (Kernel Git).

The vulnerability manifests as a race condition between the DRM scheduler workqueue and the IRQ execution thread during CPU boot sequence. The issue specifically affects the rcutasksrudewaitgp() function's call to scheduleoneachcpu(), which causes problems during early boot when only one CPU (the boot CPU) is online. The problem occurs because the cpusread_[lock/unlock] mechanism doesn't maintain a stable online CPU mask during the secondary CPU boot process (Kernel Git).

When triggered, this vulnerability can result in system warnings and potential instability during the boot process. The issue manifests as kernel warnings and can affect system stability during the initialization of secondary CPUs (Kernel Git).

The issue has been fixed by implementing a single-CPU optimization to the RCU Tasks Rude grace-period process. The fix involves adding a fastpath check in the rcutasksrudewaitgp() function that returns immediately if only one CPU is online, as there must already have been a context switch on the current CPU since the initial call (Kernel Git).