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Donenfeld" Subject: Re: [PATCH v1 3/5] treewide: use get_random_u32() when possible Message-ID: <20221006084331.4bdktc2zlvbaszym@quack3> References: <20221005214844.2699-1-Jason@zx2c4.com> <20221005214844.2699-4-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221005214844.2699-4-Jason@zx2c4.com> X-Mailman-Approved-At: Thu, 06 Oct 2022 22:26:49 +1100 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andrew Lunn , "Darrick J . Wong" , Ulf Hansson , dri-devel@lists.freedesktop.org, Andrii Nakryiko , Hans Verkuil , linux-sctp@vger.kernel.org, "Md . Haris Iqbal" , Miquel Raynal , Christoph Hellwig , Andy Gospodarek , Sergey Matyukevich , Rohit Maheshwari , ceph-devel@vger.kernel.org, Jozsef Kadlecsik , Nilesh Javali , Jean-Paul Roubelat , Dick Kennedy , Jay Vosburgh , Potnuri Bharat Teja , Vinay Kumar Yadav , linux-nfs@vger.kernel.org, Nicholas Piggin , Igor Mitsyanko , Andy Lutomirski , linux-hams@vger.kernel.org, Thomas Gleixner , Trond Myklebust , linux-raid@vger.kernel.org, Neil Horman , Hante Meuleman , Greg Kroah-Hartman , linux-usb@vger.kernel.org, Michael Chan , linux-kernel@vger.kernel.org, Varun Prakash , Chuck Lever , netfilter-devel@vger.kernel.org, Masami Hiramatsu , Jiri Olsa , Jan Kara , linux-fsdevel@vger.kernel.org, Lars Ellenberg , linux-media@vger.kernel.org, Claudiu Beznea , Sharvari Harisangam , linux-fbdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-mmc@vger.kernel.org, Dave Hansen , Song Liu , Eric Dumazet , target-devel@vger.kernel.org, John Stultz , Stanislav Fomichev , Gregory Greenman , drbd-dev@lists.linbit.com, dev@openvswitch.org, Leon Romanovsky , Helge Deller , Hugh Dickins , James Smart , Anil S Keshavamurthy , Pravin B Shelar , Julian Anastasov , coreteam@netfilter.org, Veaceslav Falico , Yonghong Song , Namjae Jeon , linux-crypto@vger.kernel.org, Santosh Shilimkar , Ganapathi Bhat , linux-actions@lists.infradead.org, Simon Horman , Jaegeuk Kim , Mika Westerberg , Andrew Morton , OGAWA Hirofumi , Hao Luo , Theodore Ts'o , Stephen Boyd , Dennis Dalessandro , Florian Westphal , Andreas =?utf-8?Q?F=C3=A4rber?= , Jon Maloy , Vlad Yasevich , Anna Schumaker , Yehezkel Bernat , Haoyue Xu , Heiner Kallweit , linux-wireless@vger.kernel.org, Marcelo Ricardo Leitner , Rasmus Villemoes , linux-nvme@lists.infradead.org, Michal Januszewski , linux-mtd@lists.infradead.org, kasan-dev@googlegroups.com, Cong Wang , Thomas Sailer , Ajay Singh , Xiubo Li , Sagi Grimberg , Daniel Borkmann , Jonathan Corbet , linux-rdma@vger.kernel.org, lvs-devel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, "Naveen N . Rao" , Ilya Dryomov , Paolo Abeni , Pablo Neira Ayuso , Marco Elver , Kees Cook , Yury Norov , "James E . J . Bottomley" , Jamal Hadi Salim , KP Singh , Borislav Petkov , Keith Busch , Dan Williams , Mauro Carvalho Chehab , Franky Lin , Arend van Spriel , linux-ext4@vger.kernel.org, Wenpeng Liang , "Martin K . Petersen" , Xinming Hu , linux-stm32@st-md-mailman.stormreply.com, Jeff Layton , linux-xfs@vger.kernel.org, netdev@vger.kernel.org, Ying Xue , Manish Rangankar , "David S . Miller" , Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= , Vi gnesh Raghavendra , Peter Zijlstra , "H . Peter Anvin" , Alexandre Torgue , Amitkumar Karwar , linux-mm@kvack.org, Andreas Dilger , Ayush Sawal , Andreas Noever , Jiri Pirko , linux-f2fs-devel@lists.sourceforge.net, Jack Wang , Steffen Klassert , rds-devel@oss.oracle.com, Herbert Xu , linux-scsi@vger.kernel.org, dccp@vger.kernel.org, Richard Weinberger , Russell King , Jaehoon Chung , Jason Gunthorpe , SHA-cyfmac-dev-list@infineon.com, Ingo Molnar , Jakub Kicinski , John Fastabend , Maxime Coquelin , Manivannan Sadhasivam , Mic hael Jamet , Kalle Valo , Chao Yu , Akinobu Mita , linux-block@vger.kernel.org, dmaengine@vger.kernel.org, Hannes Reinecke , Andy Shevchenko , Dmitry Vyukov , Jens Axboe , cake@lists.bufferbloat.net, brcm80211-dev-list.pdl@broadcom.com, Yishai Hadas , Hideaki YOSHIFUJI , linuxppc-dev@lists.ozlabs.org, David Ahern , Philipp Reisner , Stephen Hemminger , Christoph =?utf-8?Q?B=C3=B6hmwalder?= , Vinod Koul , tipc-discussion@lists.sourceforge.net, Thomas Graf , Johannes Berg , Sungjong Seo , Martin KaFai Lau Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed 05-10-22 23:48:42, Jason A. Donenfeld wrote: > The prandom_u32() function has been a deprecated inline wrapper around > get_random_u32() for several releases now, and compiles down to the > exact same code. Replace the deprecated wrapper with a direct call to > the real function. > > Signed-off-by: Jason A. Donenfeld ... > diff --git a/fs/ext2/ialloc.c b/fs/ext2/ialloc.c > index 998dd2ac8008..e439a872c398 100644 > --- a/fs/ext2/ialloc.c > +++ b/fs/ext2/ialloc.c > @@ -277,7 +277,7 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent) > int best_ndir = inodes_per_group; > int best_group = -1; > > - group = prandom_u32(); > + group = get_random_u32(); > parent_group = (unsigned)group % ngroups; > for (i = 0; i < ngroups; i++) { > group = (parent_group + i) % ngroups; The code here is effectively doing the parent_group = prandom_u32_max(ngroups); > diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c > index f73e5eb43eae..954ec9736a8d 100644 > --- a/fs/ext4/ialloc.c > +++ b/fs/ext4/ialloc.c > @@ -465,7 +465,7 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent, > ext4fs_dirhash(parent, qstr->name, qstr->len, &hinfo); > grp = hinfo.hash; > } else > - grp = prandom_u32(); > + grp = get_random_u32(); Similarly here we can use prandom_u32_max(ngroups) like: if (qstr) { ... parent_group = hinfo.hash % ngroups; } else parent_group = prandom_u32_max(ngroups); > diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c > index 9af68a7ecdcf..588cb09c5291 100644 > --- a/fs/ext4/mmp.c > +++ b/fs/ext4/mmp.c > @@ -265,7 +265,7 @@ static unsigned int mmp_new_seq(void) > u32 new_seq; > > do { > - new_seq = prandom_u32(); > + new_seq = get_random_u32(); > } while (new_seq > EXT4_MMP_SEQ_MAX); OK, here we again effectively implement prandom_u32_max(EXT4_MMP_SEQ_MAX + 1). Just presumably we didn't want to use modulo here because EXT4_MMP_SEQ_MAX is rather big and so the resulting 'new_seq' would be seriously non-uniform. Honza -- Jan Kara SUSE Labs, CR