From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f175.google.com (mail-pd0-f175.google.com [209.85.192.175]) by kanga.kvack.org (Postfix) with ESMTP id D713A6B0032 for ; Sun, 25 Jan 2015 09:38:01 -0500 (EST) Received: by mail-pd0-f175.google.com with SMTP id fl12so7171907pdb.6 for ; Sun, 25 Jan 2015 06:38:01 -0800 (PST) Received: from mail-pd0-x22a.google.com (mail-pd0-x22a.google.com. [2607:f8b0:400e:c02::22a]) by mx.google.com with ESMTPS id je7si9053106pbd.15.2015.01.25.06.38.00 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sun, 25 Jan 2015 06:38:00 -0800 (PST) Received: by mail-pd0-f170.google.com with SMTP id p10so7195006pdj.1 for ; Sun, 25 Jan 2015 06:38:00 -0800 (PST) Date: Sun, 25 Jan 2015 23:38:34 +0900 From: Sergey Senozhatsky Subject: Re: [PATCH 2/2] zram: protect zram->stat race with init_lock Message-ID: <20150125143834.GA951@swordfish> References: <1421992707-32658-1-git-send-email-minchan@kernel.org> <1421992707-32658-2-git-send-email-minchan@kernel.org> <20150123143849.GB2320@swordfish> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Ganesh Mahendran Cc: Sergey Senozhatsky , Minchan Kim , Andrew Morton , linux-kernel , Linux-MM , Nitin Gupta , Jerome Marchand Hello, On (01/24/15 21:17), Ganesh Mahendran wrote: > Hello Sergey > > 2015-01-23 22:38 GMT+08:00 Sergey Senozhatsky : > > On (01/23/15 14:58), Minchan Kim wrote: > >> The zram->stat handling should be procted by init_lock. > >> Otherwise, user could see stale value from the stat. > >> > >> Signed-off-by: Minchan Kim > >> --- > >> > >> I don't think it's stable material. The race is rare in real practice > >> and this stale stat value read is not a critical. > >> > >> drivers/block/zram/zram_drv.c | 37 ++++++++++++++++++++++++++++--------- > >> 1 file changed, 28 insertions(+), 9 deletions(-) > >> > >> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > >> index 0299d82275e7..53f176f590b0 100644 > >> --- a/drivers/block/zram/zram_drv.c > >> +++ b/drivers/block/zram/zram_drv.c > >> @@ -48,8 +48,13 @@ static ssize_t name##_show(struct device *d, \ > >> struct device_attribute *attr, char *b) \ > >> { \ > > > > a side note: I wasn't Cc'd in that patchset and found out it only when it's > > been merged. I'm not sure I understand, why it has been renamed from specific > > zram_X_show to X_show. what gives? > > I changed from zram_attr_##name##_show to name##_show in commit: > fcf1bce zram: use DEVICE_ATTR_[RW|RO|WO] to define zram sys device attribute > > I just want to keep the name consistent with others, like > disksize_show(), initstate_show(). aha, I see. -ss > Thanks. > > > > > > > can't help, catches my eye every time, that rename has broken the original > > formatting: > > > > > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > > index 9250b3f..c567af5 100644 > > --- a/drivers/block/zram/zram_drv.c > > +++ b/drivers/block/zram/zram_drv.c > > @@ -44,7 +44,7 @@ static const char *default_compressor = "lzo"; > > static unsigned int num_devices = 1; > > > > #define ZRAM_ATTR_RO(name) \ > > -static ssize_t name##_show(struct device *d, \ > > +static ssize_t name##_show(struct device *d, \ > > struct device_attribute *attr, char *b) \ > > { \ > > struct zram *zram = dev_to_zram(d); \ > > > > > > > > I don't have any objections. but do we really want to wrap atomic ops in > > semaphore? it is really such serious race? > > > > > > -ss > > > >> struct zram *zram = dev_to_zram(d); \ > >> - return scnprintf(b, PAGE_SIZE, "%llu\n", \ > >> - (u64)atomic64_read(&zram->stats.name)); \ > >> + u64 val = 0; \ > >> + \ > >> + down_read(&zram->init_lock); \ > >> + if (init_done(zram)) \ > >> + val = atomic64_read(&zram->stats.name); \ > >> + up_read(&zram->init_lock); \ > >> + return scnprintf(b, PAGE_SIZE, "%llu\n", val); \ > >> } \ > >> static DEVICE_ATTR_RO(name); > >> > >> @@ -67,8 +72,14 @@ static ssize_t disksize_show(struct device *dev, > >> struct device_attribute *attr, char *buf) > >> { > >> struct zram *zram = dev_to_zram(dev); > >> + u64 val = 0; > >> + > >> + down_read(&zram->init_lock); > >> + if (init_done(zram)) > >> + val = zram->disksize; > >> + up_read(&zram->init_lock); > >> > >> - return scnprintf(buf, PAGE_SIZE, "%llu\n", zram->disksize); > >> + return scnprintf(buf, PAGE_SIZE, "%llu\n", val); > >> } > >> > >> static ssize_t initstate_show(struct device *dev, > >> @@ -88,9 +99,14 @@ static ssize_t orig_data_size_show(struct device *dev, > >> struct device_attribute *attr, char *buf) > >> { > >> struct zram *zram = dev_to_zram(dev); > >> + u64 val = 0; > >> + > >> + down_read(&zram->init_lock); > >> + if (init_done(zram)) > >> + val = atomic64_read(&zram->stats.pages_stored) << PAGE_SHIFT; > >> + up_read(&zram->init_lock); > >> > >> - return scnprintf(buf, PAGE_SIZE, "%llu\n", > >> - (u64)(atomic64_read(&zram->stats.pages_stored)) << PAGE_SHIFT); > >> + return scnprintf(buf, PAGE_SIZE, "%llu\n", val); > >> } > >> > >> static ssize_t mem_used_total_show(struct device *dev, > >> @@ -957,10 +973,6 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector, > >> struct bio_vec bv; > >> > >> zram = bdev->bd_disk->private_data; > >> - if (!valid_io_request(zram, sector, PAGE_SIZE)) { > >> - atomic64_inc(&zram->stats.invalid_io); > >> - return -EINVAL; > >> - } > >> > >> down_read(&zram->init_lock); > >> if (unlikely(!init_done(zram))) { > >> @@ -968,6 +980,13 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector, > >> goto out_unlock; > >> } > >> > >> + if (!valid_io_request(zram, sector, PAGE_SIZE)) { > >> + atomic64_inc(&zram->stats.invalid_io); > >> + err = -EINVAL; > >> + goto out_unlock; > >> + } > >> + > >> + > >> index = sector >> SECTORS_PER_PAGE_SHIFT; > >> offset = sector & (SECTORS_PER_PAGE - 1) << SECTOR_SHIFT; > >> > >> -- > >> 1.9.1 > >> > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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