Re: [PATCH] dma: apple-admac: Convert from tasklet to BH workqueue
From: Frank Li <Frank.li@nxp.com>
Date: 2026-02-06 19:25:47
Also in:
asahi, dmaengine, lkml
On Fri, Feb 06, 2026 at 04:01:37AM -0500, Pat Somaru wrote:
The only generic interface to execute asynchronously in the BH context
is tasklet; however, it's marked deprecated and has some design flaws
such as the execution code accessing the tasklet item after the
execution is complete which can lead to subtle use-after-free in certain
usage scenarios and less-developed flush and cancel mechanisms.
To replace tasklets, BH workqueue support was recently added. A BH
workqueue behaves similarly to regular workqueues except that the queued
work items are executed in the BH context.
This patch converts drivers/dma/apple-admac.c from tasklet to BH
workqueue.
The Apple ADMAC driver uses a per-channel tasklet to invoke DMA
completion callbacks for cyclic transactions. This conversion maintains
the same execution semantics while using the modern BH workqueue
infrastructure.
This patch was tested by:
- Building with allmodconfig: no new warnings (compared to v6.18)
- Building with allyesconfig: no new warnings (compared to v6.18)
- Booting defconfig kernel via vng and running `uname -a`:
Linux virtme-ng 6.18.0-virtme #1 SMP PREEMPT_DYNAMIC 0 x86_64 GNU/Linux
Semantically, this is an equivalent conversion and there shouldn't be
any user-visible behavior changes. The BH workqueue implementation uses
the same softirq infrastructure, and performance-critical networking
conversions have shown no measurable performance impact.
Maintainers can apply this directly to the DMA subsystem tree or ack it
for the workqueue tree to carry.
Signed-off-by: Pat Somaru <redacted>
---Reviewed-by: Frank Li <Frank.Li@nxp.com>
quoted hunk ↗ jump to hunk
drivers/dma/apple-admac.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-)diff --git a/drivers/dma/apple-admac.c b/drivers/dma/apple-admac.c index bd49f0374291..8a0e100d5aaf 100644 --- a/drivers/dma/apple-admac.c +++ b/drivers/dma/apple-admac.c@@ -16,6 +16,7 @@ #include <linux/reset.h> #include <linux/spinlock.h> #include <linux/interrupt.h> +#include <linux/workqueue.h> #include "dmaengine.h"@@ -89,7 +90,7 @@ struct admac_chan { unsigned int no; struct admac_data *host; struct dma_chan chan; - struct tasklet_struct tasklet; + struct work_struct work; u32 carveout;@@ -522,8 +523,8 @@ static int admac_terminate_all(struct dma_chan *chan) adchan->current_tx = NULL; } /* - * Descriptors can only be freed after the tasklet - * has been killed (in admac_synchronize). + * Descriptors can only be freed after the work + * has been cancelled (in admac_synchronize). */ list_splice_tail_init(&adchan->submitted, &adchan->to_free); list_splice_tail_init(&adchan->issued, &adchan->to_free);@@ -543,7 +544,7 @@ static void admac_synchronize(struct dma_chan *chan) list_splice_tail_init(&adchan->to_free, &head); spin_unlock_irqrestore(&adchan->lock, flags); - tasklet_kill(&adchan->tasklet); + cancel_work_sync(&adchan->work); list_for_each_entry_safe(adtx, _adtx, &head, node) { list_del(&adtx->node);@@ -662,7 +663,7 @@ static void admac_handle_status_desc_done(struct admac_data *ad, int channo) tx->reclaimed_pos %= 2 * tx->buf_len; admac_cyclic_write_desc(ad, channo, tx); - tasklet_schedule(&adchan->tasklet); + queue_work(system_bh_wq, &adchan->work); } spin_unlock_irqrestore(&adchan->lock, flags); }@@ -712,9 +713,9 @@ static irqreturn_t admac_interrupt(int irq, void *devid) return IRQ_HANDLED; } -static void admac_chan_tasklet(struct tasklet_struct *t) +static void admac_chan_work(struct work_struct *work) { - struct admac_chan *adchan = from_tasklet(adchan, t, tasklet); + struct admac_chan *adchan = from_work(adchan, work, work); struct admac_tx *adtx; struct dmaengine_desc_callback cb; struct dmaengine_result tx_result;@@ -886,7 +887,7 @@ static int admac_probe(struct platform_device *pdev) INIT_LIST_HEAD(&adchan->issued); INIT_LIST_HEAD(&adchan->to_free); list_add_tail(&adchan->chan.device_node, &dma->channels); - tasklet_setup(&adchan->tasklet, admac_chan_tasklet); + INIT_WORK(&adchan->work, admac_chan_work); } err = reset_control_reset(ad->rstc); --2.52.0