On 10/3/24 8:31 AM, Dan Carpenter wrote: > On Thu, Oct 03, 2024 at 07:21:25AM -0600, Jens Axboe wrote: >> On 10/3/24 6:03 AM, Dan Carpenter wrote: >>> 3117 ioc_now(iocg->ioc, &now); >>> 3118 weight_updated(iocg, &now); >>> 3119 spin_unlock(&iocg->ioc->lock); >>> 3120 } >>> 3121 } >>> 3122 spin_unlock_irq(&blkcg->lock); >>> 3123 >>> 3124 return nbytes; >>> 3125 } >>> 3126 >>> 3127 blkg_conf_init(&ctx, buf); >>> 3128 >>> 3129 ret = blkg_conf_prep(blkcg, &blkcg_policy_iocost, &ctx); >>> 3130 if (ret) >>> 3131 goto err; >>> 3132 >>> 3133 iocg = blkg_to_iocg(ctx.blkg); >>> 3134 >>> 3135 if (!strncmp(ctx.body, "default", 7)) { >>> 3136 v = 0; >>> 3137 } else { >>> 3138 if (!sscanf(ctx.body, "%u", &v)) >>> 3139 goto einval; >>> 3140 if (v < CGROUP_WEIGHT_MIN || v > CGROUP_WEIGHT_MAX) >>> 3141 goto einval; >>> 3142 } >>> 3143 >>> 3144 spin_lock(&iocg->ioc->lock); >>> >>> But why is this not spin_lock_irq()? I haven't analyzed this so maybe it's >>> fine. >> >> That's a bug. >> > > I could obviously write this patch but I feel stupid writing the > commit message. My level of understanding is Monkey See Monkey do. > Could you take care of this? Sure - or let's add Tejun who knows this code better. Ah he's already added. Tejun? > So somewhere we're taking a lock in the IRQ handler and this can lead > to a deadlock? I thought this would have been caught by lockdep? It's nested inside blkcg->lock which is IRQ safe, that is enough. But doing a quick scan of the file, the usage is definitely (widly) inconsistent. Most times ioc->lock is grabbed disabling interrupts, but there are also uses that doesn't disable interrupts, coming from things like seq_file show paths which certainly look like they need it. lockdep should certainly warn about this, only explanation I have is that nobody bothered to do that :-) -- Jens Axboe