From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f50.google.com (mail-ej1-f50.google.com [209.85.218.50]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4151972 for ; Sun, 29 Aug 2021 09:23:00 +0000 (UTC) Received: by mail-ej1-f50.google.com with SMTP id me10so24016792ejb.11 for ; Sun, 29 Aug 2021 02:23:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=e+dqt6XS4ZNHrivjUXrH9fxmNodvBLxJ0+D0nFk09Hs=; b=JU8XOd2b7Xq5IKjUsiaaBVKqQ3ZtsFJwsPoNIih8o+KUk46lR4ecr611my62NK94Z5 cLZlHegUnhQo6eN7sxiYLPLd8CIrtDYVLdwdtExbixGnYWFDEtkzsa11hQ/XG2rPr6mj RFadpuwGKvGyQGDZtydcVxY6RyAFMU1Tw44uD4EZhKQhbEUw4IVrdf0EK0tkinCyvFCO +lotJf7sryrklWXPjz0BHrU88LxcL6cgcP6lFcUZCXcQFP2d9RNBKMCdmK/CvckqjQwJ 98Zcc5y4MDfDcgf5akQMDpnikq15HZn3lw+PvDjhQNydQomY60Im6u5BjleJdZ2rEZmX bUdg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=e+dqt6XS4ZNHrivjUXrH9fxmNodvBLxJ0+D0nFk09Hs=; b=lzPS8y70bdAVa9pAxME6beMhTKzOXXHHLHqrfmETRN9jFWekjTSETO6z+jLjYojJ37 Yr8+ziQEJsrGi3oRpRvBYQ8kOxwK/DLdMSANgLd6VYDmprJQ4ahg3YTloTqNahC58ydC XrIgB7NJUEvSZszZlP1mBaN867xepGYzXV4KHFnaUc994qTKr0AkVUdTcyvshnD63bZ7 3RjHpRowYH5n3lKDBFvKtbSrIXjozTAhkDINSPOxMwC3eAkM7tQ1zlqbE7B7hPk5hpGS asznSwNZLh+tGtP0jFqLn1KeYZNTDzsCb13vg291PVT2kzqYf34ivMY3XHGp+CiOI2n5 VFlA== X-Gm-Message-State: AOAM531epzknXLSsXN4xOxY11nqyhRWgEPmX9ccqwgeb4laZ/ZWlzaY2 GZFsSVMBtOO54XQXg8/gMxM= X-Google-Smtp-Source: ABdhPJy6D7wvo+5iCtrPdFblc/OhtL1DNGesRrmldOnErYS5oePwvizVmEzgWREo4pwFRIlztOd93g== X-Received: by 2002:a17:907:628d:: with SMTP id nd13mr19549239ejc.7.1630228978627; Sun, 29 Aug 2021 02:22:58 -0700 (PDT) Received: from localhost.localdomain (host-79-22-100-164.retail.telecomitalia.it. [79.22.100.164]) by smtp.gmail.com with ESMTPSA id u4sm610916ejc.19.2021.08.29.02.22.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 29 Aug 2021 02:22:57 -0700 (PDT) From: "Fabio M. De Francesco" To: Johan Hovold , Alex Elder , Greg Kroah-Hartman , greybus-dev@lists.linaro.org, linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org Cc: "Fabio M. De Francesco" Subject: [PATCH v4] staging: greybus: Convert uart.c from IDR to XArray Date: Sun, 29 Aug 2021 11:22:50 +0200 Message-Id: <20210829092250.25379-1-fmdefrancesco@gmail.com> X-Mailer: git-send-email 2.32.0 Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Convert greybus/uart.c from IDR to XArray. The abstract data type XArray is more memory-efficient, parallelisable, and cache friendly. It takes advantage of RCU to perform lookups without locking. Furthermore, IDR is deprecated because XArray has a better (cleaner and more consistent) API. Signed-off-by: Fabio M. De Francesco --- v3->v4: Remove mutex_lock/unlock around xa_load(). These locks seem to be unnecessary because there is a 1:1 correspondence between a specific minor and its gb_tty and there is no reference counting. I think that the RCU locks used inside xa_load() are sufficient to protect this API from returning an invalid gb_tty in case of concurrent access. Some more considerations on this topic are in the following message to linux-kernel list: https://lore.kernel.org/lkml/3554184.2JXonMZcNW@localhost.localdomain/ v2->v3: Fix some issues according to a review by Alex Elder v1->v2: Fix an issue found by the kernel test robot. It is due to passing to xa_*lock() the same old mutex that IDR used with the previous version of the code. drivers/staging/greybus/uart.c | 32 ++++++++++++++------------------ 1 file changed, 14 insertions(+), 18 deletions(-) diff --git a/drivers/staging/greybus/uart.c b/drivers/staging/greybus/uart.c index 73f01ed1e5b7..f66983adb51b 100644 --- a/drivers/staging/greybus/uart.c +++ b/drivers/staging/greybus/uart.c @@ -22,7 +22,7 @@ #include #include #include -#include +#include #include #include #include @@ -32,8 +32,9 @@ #include "gbphy.h" -#define GB_NUM_MINORS 16 /* 16 is more than enough */ -#define GB_NAME "ttyGB" +#define GB_NUM_MINORS 16 /* 16 is more than enough */ +#define GB_RANGE_MINORS XA_LIMIT(0, GB_NUM_MINORS) +#define GB_NAME "ttyGB" #define GB_UART_WRITE_FIFO_SIZE PAGE_SIZE #define GB_UART_WRITE_ROOM_MARGIN 1 /* leave some space in fifo */ @@ -67,8 +68,7 @@ struct gb_tty { }; static struct tty_driver *gb_tty_driver; -static DEFINE_IDR(tty_minors); -static DEFINE_MUTEX(table_lock); +static DEFINE_XARRAY(tty_minors); static int gb_uart_receive_data_handler(struct gb_operation *op) { @@ -341,8 +341,7 @@ static struct gb_tty *get_gb_by_minor(unsigned int minor) { struct gb_tty *gb_tty; - mutex_lock(&table_lock); - gb_tty = idr_find(&tty_minors, minor); + gb_tty = xa_load(&tty_minors, minor); if (gb_tty) { mutex_lock(&gb_tty->mutex); if (gb_tty->disconnected) { @@ -353,19 +352,18 @@ static struct gb_tty *get_gb_by_minor(unsigned int minor) mutex_unlock(&gb_tty->mutex); } } - mutex_unlock(&table_lock); return gb_tty; } static int alloc_minor(struct gb_tty *gb_tty) { int minor; + int ret; - mutex_lock(&table_lock); - minor = idr_alloc(&tty_minors, gb_tty, 0, GB_NUM_MINORS, GFP_KERNEL); - mutex_unlock(&table_lock); - if (minor >= 0) - gb_tty->minor = minor; + ret = xa_alloc(&tty_minors, &minor, gb_tty, GB_RANGE_MINORS, GFP_KERNEL); + if (ret) + return ret; + gb_tty->minor = minor; return minor; } @@ -374,9 +372,7 @@ static void release_minor(struct gb_tty *gb_tty) int minor = gb_tty->minor; gb_tty->minor = 0; /* Maybe should use an invalid value instead */ - mutex_lock(&table_lock); - idr_remove(&tty_minors, minor); - mutex_unlock(&table_lock); + xa_erase(&tty_minors, minor); } static int gb_tty_install(struct tty_driver *driver, struct tty_struct *tty) @@ -837,7 +833,7 @@ static int gb_uart_probe(struct gbphy_device *gbphy_dev, minor = alloc_minor(gb_tty); if (minor < 0) { - if (minor == -ENOSPC) { + if (minor == -EBUSY) { dev_err(&gbphy_dev->dev, "no more free minor numbers\n"); retval = -ENODEV; @@ -982,7 +978,7 @@ static void gb_tty_exit(void) { tty_unregister_driver(gb_tty_driver); put_tty_driver(gb_tty_driver); - idr_destroy(&tty_minors); + xa_destroy(&tty_minors); } static const struct gbphy_device_id gb_uart_id_table[] = { -- 2.32.0