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Sat, 28 Feb 2026 16:58:38 -0800 (PST) Received: from instance-20260207-1316.vcn12250046.oraclevcn.com ([150.136.248.187]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-899e845bf7asm17368196d6.40.2026.02.28.16.58.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 28 Feb 2026 16:58:37 -0800 (PST) From: Josh Law X-Google-Original-From: Josh Law To: Greg Kroah-Hartman Cc: linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, Josh Law Subject: [PATCH] staging: axis-fifo: minimize lock duration in write Date: Sun, 1 Mar 2026 00:58:36 +0000 Message-ID: <20260301005836.2513391-1-objecting@objecting.org> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Memory allocation and copy from user space with vmemdup_user() is relativel= y slow and can sleep. Move it outside the lock to minimize the time the mut= ex 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-f= ifo/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 c= har __user *buf, (words_to_write > (fifo->tx_fifo_depth - 4))) return -EINVAL; =20 + txbuf =3D 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 =3D -EAGAIN; + goto err_free; + } =20 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; } =20 - txbuf =3D vmemdup_user(buf, len); - if (IS_ERR(txbuf)) { - ret =3D PTR_ERR(txbuf); - goto end_unlock; - } - for (int i =3D 0; i < words_to_write; ++i) iowrite32(txbuf[i], fifo->base_addr + XLLF_TDFD_OFFSET); =20 iowrite32(len, fifo->base_addr + XLLF_TLR_OFFSET); =20 ret =3D len; - kvfree(txbuf); + end_unlock: mutex_unlock(&fifo->write_lock); +err_free: + kvfree(txbuf); =20 return ret; } --=20 2.43.0