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Mon, 19 Feb 2024 18:06:42 +0000 (UTC) Received: from dovecot-director2.suse.de ([10.150.64.162]) by imap2.dmz-prg2.suse.org with ESMTPSA id ZU+VD7KY02WoRAAAn2gu4w (envelope-from ); Mon, 19 Feb 2024 18:06:42 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id DBDFCA0807; Mon, 19 Feb 2024 19:06:41 +0100 (CET) Date: Mon, 19 Feb 2024 19:06:41 +0100 From: Jan Kara To: "Liam R. Howlett" Cc: Jan Kara , Chuck Lever , viro@zeniv.linux.org.uk, brauner@kernel.org, hughd@google.com, akpm@linux-foundation.org, oliver.sang@intel.com, feng.tang@intel.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, maple-tree@lists.infradead.org, linux-mm@kvack.org, lkp@intel.com Subject: Re: [PATCH RFC 7/7] libfs: Re-arrange locking in offset_iterate_dir() Message-ID: <20240219180641.hdd5q2vvx5sixuh6@quack3> References: <170785993027.11135.8830043889278631735.stgit@91.116.238.104.host.secureserver.net> <170786028847.11135.14775608389430603086.stgit@91.116.238.104.host.secureserver.net> <20240215131638.cxipaxanhidb3pev@quack3> <20240215170008.22eisfyzumn5pw3f@revolver> <20240215171622.gsbjbjz6vau3emkh@quack3> <20240215210742.grjwdqdypvgrpwih@revolver> <20240216101546.xjcpzyb3pgf2eqm4@quack3> <20240216163318.w66ywrhpr5at46pi@revolver> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240216163318.w66ywrhpr5at46pi@revolver> X-Rspam-User: X-Stat-Signature: tq9mmm5btd77wnkck1wtow5iwz15zo38 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 9937FC001E X-HE-Tag: 1708366006-380833 X-HE-Meta: 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 hbukN1ok 9lIu5/E+eiiXb109ipqCdxS1hg0Y71RLCsSuKNuwJLbHW86YFXZU3lQ7eoi+9+hDCP9Y1ta1mRw/J2ganEqohgAAr+z3LcjDZ6A8quP2eriK/kL/zp9z+QL+y58iIwDzlFztFWiV8XYfzDIR2b0XJFnZE8eB61BXVZHW3p5wctG2VLyjDznNnQcjfauRfPHsIcYtLgEP4OEVoCRfs3AswKyUxp/HFDygqXW8ZCRnHv44/IZOao3/O8GrAnoo0KhwyWFxLplrvM3WCblYrp6CkzUZVnRgjlnJV70H6e10g9mDhYsU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri 16-02-24 11:33:18, Liam R. Howlett wrote: > * Jan Kara [240216 05:15]: > > > If you have other examples you think are unsafe then I can have a look > > > at them as well. > > > > I'm currently not aware of any but I'll let you know if I find some. > > Missing xas/mas_pause() seems really easy. > > What if we convert the rcu_read_lock() to a mas_read_lock() or > xas_read_lock() and we can check to ensure the state isn't being locked > without being in the 'parked' state (paused or otherwise)? > > mas_read_lock(struct ma_state *mas) { > assert(!mas_active(mas)); > rcu_read_lock(); > } > > Would that be a reasonable resolution to your concern? Unfortunately, > what was done with the locking in this case would not be detected with > this change unless the rcu_read_lock() was replaced. IOW, people could > still use the rcu_read_lock() and skip the detection. Yes, I guess this is still better than nothing. > Doing the same in the mas_unlock() doesn't make as much sense since that > may be called without the intent to reuse the state at all. So we'd be > doing more work than necessary at the end of each loop or use. Yes, understood. Honza -- Jan Kara SUSE Labs, CR