tick/rcu: Fix false positive "softirq work is pending" messages #172
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commit 96c1fa0 upstream. In commit 0345691 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle") the new function report_idle_softirq() was created by breaking code out of the existing can_stop_idle_tick() for kernels v5.18 and newer. In doing so, the code essentially went from a one conditional: if (a && b && c) warn(); to a three conditional: if (!a) return; if (!b) return; if (!c) return; warn(); But that conversion got the condition for the RT specific local_bh_blocked() wrong. The original condition was: !local_bh_blocked() but the conversion failed to negate it so it ended up as: if (!local_bh_blocked()) return false; This issue lay dormant until another fixup for the same commit was added in commit a7e282c ("tick/rcu: Fix bogus ratelimit condition"). This commit realized the ratelimit was essentially set to zero instead of ten, and hence *no* softirq pending messages would ever be issued. Once this commit was backported via linux-stable, both the v6.1 and v6.4 preempt-rt kernels started printing out 10 instances of this at boot: NOHZ tick-stop error: local softirq work is pending, handler RevolutionPi#80!!! Remove the negation and return when local_bh_blocked() evaluates to true to bring the correct behaviour back. Fixes: 0345691 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle") Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Ahmad Fatoum <a.fatoum@pengutronix.de> Reviewed-by: Wen Yang <wenyang.linux@foxmail.com> Acked-by: Frederic Weisbecker <frederic@kernel.org> Link: https://lore.kernel.org/r/20230818200757.1808398-1-paul.gortmaker@windriver.com
l1k
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iluminat23
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commit 96c1fa0 upstream.
In commit 0345691 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle") the new function report_idle_softirq() was created by breaking code out of the existing can_stop_idle_tick() for kernels v5.18 and newer.
In doing so, the code essentially went from a one conditional:
to a three conditional:
But that conversion got the condition for the RT specific local_bh_blocked() wrong. The original condition was:
but the conversion failed to negate it so it ended up as:
This issue lay dormant until another fixup for the same commit was added in commit a7e282c ("tick/rcu: Fix bogus ratelimit condition"). This commit realized the ratelimit was essentially set to zero instead of ten, and hence no softirq pending messages would ever be issued.
Once this commit was backported via linux-stable, both the v6.1 and v6.4 preempt-rt kernels started printing out 10 instances of this at boot:
NOHZ tick-stop error: local softirq work is pending, handler #80!!!
Remove the negation and return when local_bh_blocked() evaluates to true to bring the correct behaviour back.
Fixes: 0345691 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle")
Tested-by: Ahmad Fatoum a.fatoum@pengutronix.de
Reviewed-by: Wen Yang wenyang.linux@foxmail.com
Acked-by: Frederic Weisbecker frederic@kernel.org
Link: https://lore.kernel.org/r/20230818200757.1808398-1-paul.gortmaker@windriver.com