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Fri, 18 Sep 2020 06:53:37 -0400 X-MC-Unique: o8KaCKCnMIyeWdkQtmzwNg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 83B12104D3E5; Fri, 18 Sep 2020 10:53:35 +0000 (UTC) Received: from [10.36.110.9] (unknown [10.36.110.9]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F05DB7881F; Fri, 18 Sep 2020 10:53:32 +0000 (UTC) To: Vipul Ashri , Edward Makarov , Andrew Rybchenko , dev@dpdk.org Cc: chenbo.xia@intel.com, zhihong.wang@intel.com, stable@dpdk.org References: <20200814092138.1692-1-vipul.ashri@oracle.com> <7a2d66d6-3961-5251-36d2-c702fe80379f@solarflare.com> <1b510ced-ba3a-4bf9-8d33-204073cfedba@default> From: Maxime Coquelin Autocrypt: addr=maxime.coquelin@redhat.com; keydata= mQINBFOEQQIBEADjNLYZZqghYuWv1nlLisptPJp+TSxE/KuP7x47e1Gr5/oMDJ1OKNG8rlNg kLgBQUki3voWhUbMb69ybqdMUHOl21DGCj0BTU3lXwapYXOAnsh8q6RRM+deUpasyT+Jvf3a gU35dgZcomRh5HPmKMU4KfeA38cVUebsFec1HuJAWzOb/UdtQkYyZR4rbzw8SbsOemtMtwOx YdXodneQD7KuRU9IhJKiEfipwqk2pufm2VSGl570l5ANyWMA/XADNhcEXhpkZ1Iwj3TWO7XR uH4xfvPl8nBsLo/EbEI7fbuUULcAnHfowQslPUm6/yaGv6cT5160SPXT1t8U9QDO6aTSo59N jH519JS8oeKZB1n1eLDslCfBpIpWkW8ZElGkOGWAN0vmpLfdyiqBNNyS3eGAfMkJ6b1A24un /TKc6j2QxM0QK4yZGfAxDxtvDv9LFXec8ENJYsbiR6WHRHq7wXl/n8guyh5AuBNQ3LIK44x0 KjGXP1FJkUhUuruGyZsMrDLBRHYi+hhDAgRjqHgoXi5XGETA1PAiNBNnQwMf5aubt+mE2Q5r qLNTgwSo2dpTU3+mJ3y3KlsIfoaxYI7XNsPRXGnZi4hbxmeb2NSXgdCXhX3nELUNYm4ArKBP LugOIT/zRwk0H0+RVwL2zHdMO1Tht1UOFGfOZpvuBF60jhMzbQARAQABtCxNYXhpbWUgQ29x dWVsaW4gPG1heGltZS5jb3F1ZWxpbkByZWRoYXQuY29tPokCOAQTAQIAIgUCV3u/5QIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQyjiNKEaHD4ma2g/+P+Hg9WkONPaY1J4AR7Uf kBneosS4NO3CRy0x4WYmUSLYMLx1I3VH6SVjqZ6uBoYy6Fs6TbF6SHNc7QbB6Qjo3neqnQR1 71Ua1MFvIob8vUEl3jAR/+oaE1UJKrxjWztpppQTukIk4oJOmXbL0nj3d8dA2QgHdTyttZ1H xzZJWWz6vqxCrUqHU7RSH9iWg9R2iuTzii4/vk1oi4Qz7y/q8ONOq6ffOy/t5xSZOMtZCspu Mll2Szzpc/trFO0pLH4LZZfz/nXh2uuUbk8qRIJBIjZH3ZQfACffgfNefLe2PxMqJZ8mFJXc RQO0ONZvwoOoHL6CcnFZp2i0P5ddduzwPdGsPq1bnIXnZqJSl3dUfh3xG5ArkliZ/++zGF1O wvpGvpIuOgLqjyCNNRoR7cP7y8F24gWE/HqJBXs1qzdj/5Hr68NVPV1Tu/l2D1KMOcL5sOrz 2jLXauqDWn1Okk9hkXAP7+0Cmi6QwAPuBT3i6t2e8UdtMtCE4sLesWS/XohnSFFscZR6Vaf3 gKdWiJ/fW64L6b9gjkWtHd4jAJBAIAx1JM6xcA1xMbAFsD8gA2oDBWogHGYcScY/4riDNKXi lw92d6IEHnSf6y7KJCKq8F+Jrj2BwRJiFKTJ6ChbOpyyR6nGTckzsLgday2KxBIyuh4w+hMq TGDSp2rmWGJjASq5Ag0EVPSbkwEQAMkaNc084Qvql+XW+wcUIY+Dn9A2D1gMr2BVwdSfVDN7 0ZYxo9PvSkzh6eQmnZNQtl8WSHl3VG3IEDQzsMQ2ftZn2sxjcCadexrQQv3Lu60Tgj7YVYRM H+fLYt9W5YuWduJ+FPLbjIKynBf6JCRMWr75QAOhhhaI0tsie3eDsKQBA0w7WCuPiZiheJaL 4MDe9hcH4rM3ybnRW7K2dLszWNhHVoYSFlZGYh+MGpuODeQKDS035+4H2rEWgg+iaOwqD7bg CQXwTZ1kSrm8NxIRVD3MBtzp9SZdUHLfmBl/tLVwDSZvHZhhvJHC6Lj6VL4jPXF5K2+Nn/Su CQmEBisOmwnXZhhu8ulAZ7S2tcl94DCo60ReheDoPBU8PR2TLg8rS5f9w6mLYarvQWL7cDtT d2eX3Z6TggfNINr/RTFrrAd7NHl5h3OnlXj7PQ1f0kfufduOeCQddJN4gsQfxo/qvWVB7PaE 1WTIggPmWS+Xxijk7xG6x9McTdmGhYaPZBpAxewK8ypl5+yubVsE9yOOhKMVo9DoVCjh5To5 aph7CQWfQsV7cd9PfSJjI2lXI0dhEXhQ7lRCFpf3V3mD6CyrhpcJpV6XVGjxJvGUale7+IOp sQIbPKUHpB2F+ZUPWds9yyVxGwDxD8WLqKKy0WLIjkkSsOb9UBNzgRyzrEC9lgQ/ABEBAAGJ Ah8EGAECAAkFAlT0m5MCGwwACgkQyjiNKEaHD4nU8hAAtt0xFJAy0sOWqSmyxTc7FUcX+pbD KVyPlpl6urKKMk1XtVMUPuae/+UwvIt0urk1mXi6DnrAN50TmQqvdjcPTQ6uoZ8zjgGeASZg jj0/bJGhgUr9U7oG7Hh2F8vzpOqZrdd65MRkxmc7bWj1k81tOU2woR/Gy8xLzi0k0KUa8ueB iYOcZcIGTcs9CssVwQjYaXRoeT65LJnTxYZif2pfNxfINFzCGw42s3EtZFteczClKcVSJ1+L +QUY/J24x0/ocQX/M1PwtZbB4c/2Pg/t5FS+s6UB1Ce08xsJDcwyOPIH6O3tccZuriHgvqKP yKz/Ble76+NFlTK1mpUlfM7PVhD5XzrDUEHWRTeTJSvJ8TIPL4uyfzhjHhlkCU0mw7Pscyxn DE8G0UYMEaNgaZap8dcGMYH/96EfE5s/nTX0M6MXV0yots7U2BDb4soLCxLOJz4tAFDtNFtA wLBhXRSvWhdBJZiig/9CG3dXmKfi2H+wdUCSvEFHRpgo7GK8/Kh3vGhgKmnnxhl8ACBaGy9n fxjSxjSO6rj4/MeenmlJw1yebzkX8ZmaSi8BHe+n6jTGEFNrbiOdWpJgc5yHIZZnwXaW54QT UhhSjDL1rV2B4F28w30jYmlRmm2RdN7iCZfbyP3dvFQTzQ4ySquuPkIGcOOHrvZzxbRjzMx1 Mwqu3GQ= Message-ID: Date: Fri, 18 Sep 2020 12:53:30 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <1b510ced-ba3a-4bf9-8d33-204073cfedba@default> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=maxime.coquelin@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Subject: Re: [dpdk-dev] [PATCH] net/virtio: fix wrong variable assignment in helper macro X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On 9/18/20 12:46 PM, Vipul Ashri wrote: > Hi Edward / Andrew > > I like your suggestions and applied with [v5] net/virtio: fix wrong variable assignment in helper macro > V4 had a extra line typos., V5 is tested compiled and pushed carefully Thanks! Thanks Vipul, I plan to pick your patch later today. So I will assume Andrew still ack the patch since v5 is only fixing build. Thanks, Maxime > Regards > Vipul > > -----Original Message----- > From: Edward Makarov [mailto:makarov@kraftway.ru] > Sent: Sunday, 30 August, 2020 3:48 > To: Andrew Rybchenko ; Vipul Ashri ; dev@dpdk.org > Cc: chenbo.xia@intel.com; zhihong.wang@intel.com; maxime.coquelin@redhat.com; stable@dpdk.org > Subject: Re: [dpdk-dev] [PATCH] net/virtio: fix wrong variable assignment in helper macro > > > On 8/29/20 2:22 PM, Andrew Rybchenko wrote: >> On 8/14/20 12:21 PM, Vipul Ashri wrote: >>> Inside Macro ASSIGN_UNLESS_EQUAL(var, val), assignment to var is >>> always failing as assignment done using var_ having local scope only. >>> This leads to TX packets not going out and found broken due to >>> cleanup malfunctioning. This patch fixes the wrong variable assignment. >>> >>> Fixes: 57f90f894588 ("net/virtio: reuse packed ring functions") >>> Cc: stable@dpdk.org >>> >>> Signed-off-by: Vipul Ashri >>> --- >>> drivers/net/virtio/virtqueue.h | 6 ++---- >>> 1 file changed, 2 insertions(+), 4 deletions(-) >>> >>> diff --git a/drivers/net/virtio/virtqueue.h >>> b/drivers/net/virtio/virtqueue.h index 105a9c00c..20c95471e 100644 >>> --- a/drivers/net/virtio/virtqueue.h >>> +++ b/drivers/net/virtio/virtqueue.h >>> @@ -607,10 +607,8 @@ virtqueue_notify(struct virtqueue *vq) >>> >>> /* avoid write operation when necessary, to lessen cache issues */ >>> #define ASSIGN_UNLESS_EQUAL(var, val) do { \ >>> - typeof(var) var_ = (var); \ >>> - typeof(val) val_ = (val); \ >>> - if ((var_) != (val_)) \ >>> - (var_) = (val_); \ >>> + if ((var) != (val)) \ >>> + (var) = (val); \ >> >> Good catch. As I understand the old code tries to avoid processing of >> var and val expressions twice. It looks it could be kept for val at >> least. Just keep if condition as in old code and fix the last line >> above: >>     (var) = val_; >> Since var_ and val_are local variables there is no necessity to >> enclose it in parenthesis (but does not harm if done). >> var_ may be really removed since since resulting code will use it only >> once. > > I think there is a solution to avoid multiple evaluations of parameters: > > // var is definitely an lvalue, so its address can definitely be taken #define ASSIGN_UNLESS_EQUAL(var, val) do { \ > typeof(var) *const var_ = &(var); \ > typeof(val) const val_ = (val); \ > if (*var_ != val_) \ > *var_ = val_; \ > } while (0) > > The solution relies on the compiler optimizer. Here is the comparison of what the variants are compiled into: > > https://urldefense.com/v3/__https://godbolt.org/z/nnvq5q__;!!GqivPVa7Brio!MJZCNAgcCHB5A_T1mI2aA-2F9wvqh_WOfzkeN0IbDnsZSlNIPWqDF0b4YDmTc19HcA$ >