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Sun, 01 Mar 2026 13:48:28 -0800 (PST) From: Josh Law X-Google-Original-From: Josh Law To: Greg Kroah-Hartman , Ovidiu Panait Cc: Gabriel Shahrouzi , linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, Josh Law Subject: [PATCH v2 06/10] staging: axis-fifo: minimize lock duration in write Date: Sun, 1 Mar 2026 21:48:11 +0000 Message-ID: <20260301214815.2628942-6-objecting@objecting.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260301214815.2628942-1-objecting@objecting.org> References: <20260301214815.2628942-1-objecting@objecting.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Josh Law Memory allocation and copy from user space with vmemdup_user() is relatively slow and can sleep. Move it outside the lock to minimize the time the mutex is held, reducing contention for concurrent accesses. Signed-off-by: Josh Law --- drivers/staging/axis-fifo/axis-fifo.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/drivers/staging/axis-fifo/axis-fifo.c b/drivers/staging/axis-fifo/axis-fifo.c index aad2206b481a..d5533235cefc 100644 --- a/drivers/staging/axis-fifo/axis-fifo.c +++ b/drivers/staging/axis-fifo/axis-fifo.c @@ -233,9 +233,15 @@ static ssize_t axis_fifo_write(struct file *f, const char __user *buf, (words_to_write > (fifo->tx_fifo_depth - 4))) return -EINVAL; + txbuf = vmemdup_user(buf, len); + if (IS_ERR(txbuf)) + return PTR_ERR(txbuf); + if (f->f_flags & O_NONBLOCK) { - if (!mutex_trylock(&fifo->write_lock)) - return -EAGAIN; + if (!mutex_trylock(&fifo->write_lock)) { + ret = -EAGAIN; + goto err_free; + } if (words_to_write > ioread32(fifo->base_addr + XLLF_TDFV_OFFSET)) { @@ -252,21 +258,17 @@ static ssize_t axis_fifo_write(struct file *f, const char __user *buf, goto end_unlock; } - txbuf = vmemdup_user(buf, len); - if (IS_ERR(txbuf)) { - ret = PTR_ERR(txbuf); - goto end_unlock; - } - for (int i = 0; i < words_to_write; ++i) iowrite32(txbuf[i], fifo->base_addr + XLLF_TDFD_OFFSET); iowrite32(len, fifo->base_addr + XLLF_TLR_OFFSET); ret = len; - kvfree(txbuf); + end_unlock: mutex_unlock(&fifo->write_lock); +err_free: + kvfree(txbuf); return ret; } -- 2.43.0