Re: [PATCH 2/2] block: Convert BDI proportion calculations to flexible proportions
From: Fengguang Wu <hidden>
Date: 2012-06-01 03:10:20
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On Fri, Jun 01, 2012 at 12:42:06AM +0200, Jan Kara wrote:
On Fri 01-06-12 00:26:05, Peter Zijlstra wrote:quoted
On Fri, 2012-06-01 at 00:11 +0200, Jan Kara wrote:quoted
bool fprop_new_period(struct fprop_global *p, int periods) { - u64 events = percpu_counter_sum(&p->events); + u64 events; + unsigned long flags; + local_irq_save(flags); + events = percpu_counter_sum(&p->events); + local_irq_restore(flags); /* * Don't do anything if there are no events. */@@ -73,7 +77,9 @@ bool fprop_new_period(struct fprop_global *p, int periods) if (periods < 64) events -= events >> periods; /* Use addition to avoid losing events happening between sum and set */ + local_irq_save(flags); percpu_counter_add(&p->events, -events); + local_irq_restore(flags); p->period += periods; write_seqcount_end(&p->sequence);Uhm, why bother enabling it in between? Just wrap the whole function in a single IRQ disable.I wanted to have interrupts disabled for as short as possible but if you think it doesn't matter, I'll take your advice. The result is attached.
Thank you! I applied this incremental fix next to the commit "lib: Proportions with flexible period". Thanks, Fengguang
quoted hunk ↗ jump to hunk
From: Jan Kara <jack@suse.cz> Subject: lib: Fix possible deadlock in flexible proportion code When percpu counter function in fprop_new_period() is interrupted by an interrupt while holding counter lock, it can cause deadlock when the interrupt wants to take the lock as well. Fix the problem by disabling interrupts when calling percpu counter functions. Signed-off-by: Jan Kara <jack@suse.cz> diff -u b/lib/flex_proportions.c b/lib/flex_proportions.c--- b/lib/flex_proportions.c +++ b/lib/flex_proportions.c@@ -62,13 +62,18 @@ */ bool fprop_new_period(struct fprop_global *p, int periods) { - u64 events = percpu_counter_sum(&p->events); + u64 events; + unsigned long flags; + local_irq_save(flags); + events = percpu_counter_sum(&p->events); /* * Don't do anything if there are no events. */ - if (events <= 1) + if (events <= 1) { + local_irq_restore(flags); return false; + } write_seqcount_begin(&p->sequence); if (periods < 64) events -= events >> periods;@@ -76,6 +81,7 @@ percpu_counter_add(&p->events, -events); p->period += periods; write_seqcount_end(&p->sequence); + local_irq_restore(flags); return true; }
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