i2c: core: Run atomic i2c xfer when !preemptible

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: i2c: core: Run atomic i2c xfer when !preemptible Since bae1d3a05a8b, i2c transfers are non-atomic if preemption is disabled. However, non-atomic i2c transfers require preemption (e.g. in wait_for_completion() while waiting for the DMA). panic() calls preempt_disable_notrace() before calling emergency_restart(). Therefore, if an i2c device is used for the restart, the xfer should be atomic. This avoids warnings like: [ 12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0 [ 12.676926] Voluntary context switch within RCU read-side critical section! ... [ 12.742376] schedule_timeout from wait_for_completion_timeout+0x90/0x114 [ 12.749179] wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70 ... [ 12.994527] atomic_notifier_call_chain from machine_restart+0x34/0x58 [ 13.001050] machine_restart from panic+0x2a8/0x32c Use !preemptible() instead, which is basically the same check as pre-v5.2.

References

• https://git.kernel.org/stable/c/25eb381a736e7ae39a4245ef5c96484eb1073809
• https://git.kernel.org/stable/c/25284c46b657f48c0f3880a2e0706c70d81182c0
• https://git.kernel.org/stable/c/f6237afabc349c1c7909db00e15d2816519e0d2b
• https://git.kernel.org/stable/c/185f3617adc8fe45e40489b458f03911f0dec46c
• https://git.kernel.org/stable/c/8c3fa52a46ff4d208cefb1a462ec94e0043a91e1
• https://git.kernel.org/stable/c/3473cf43b9068b9dfef2f545f833f33c6a544b91
• https://git.kernel.org/stable/c/aa49c90894d06e18a1ee7c095edbd2f37c232d02