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a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1738572122; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zMhCIlOH9NIe7h5EnD+8+3/+PiMl7AWO2+4/9VnEWp4=; b=dMrAk6Kj3CzFRFp8ks+pDXOWRYOzLtTvurvFSjv+oYhLr7GRihr7nAkj2QEtUdQf03hGxf oLsp9PiBcLttWy12cRiCFvmwfJjiU8eNV9u3fay48O+3QXKhelO7vFfUW460QsJv2ekoHd dCGXp8eck1ptZnUMInRegnhMBi/93Ls= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1738572122; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zMhCIlOH9NIe7h5EnD+8+3/+PiMl7AWO2+4/9VnEWp4=; b=5C2qnMQttcfXV8+R0RukR0YGvicOCV9/PY00IjDdNsMe+XRTsMneOsi8FTqE/OT4pW60oU uh3/nSNKu/zRPPBA== Received: by hawking.nue2.suse.org (Postfix, from userid 17005) id AC2614A0551; Mon, 3 Feb 2025 09:42:02 +0100 (CET) From: Andreas Schwab To: David Laight Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] riscv/atomic: Do proper sign extension also for unsigned in arch_cmpxchg In-Reply-To: <20250130213504.285b4675@pumpkin> (David Laight's message of "Thu, 30 Jan 2025 21:35:04 +0000") References: <20250130213504.285b4675@pumpkin> Date: Mon, 03 Feb 2025 09:42:02 +0100 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-Spam-Score: -4.19 X-Spamd-Result: default: False [-4.19 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.19)[-0.964]; RCVD_NO_TLS_LAST(0.10)[]; MIME_GOOD(-0.10)[text/plain]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; RCVD_COUNT_ONE(0.00)[1]; TO_DN_SOME(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; TAGGED_RCPT(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:email] X-Spam-Flag: NO X-Spam-Level: On Jan 30 2025, David Laight wrote: > On Thu, 30 Jan 2025 10:25:38 +0100 > Andreas Schwab wrote: > >> Sign extend also an unsigned compare value to match what lr.w is doing. >> Otherwise try_cmpxchg may spuriously return true when used on a u32 value >> that has the sign bit set, as it happens often in inode_set_ctime_current. >> >> Do this in three conversion steps. The first conversion to long is needed >> to avoid a -Wpointer-to-int-cast warning when arch_cmpxchg is used with a >> pointer type. > > Doesn't that break things by discarding the high bits of a pointer value? If you have 32-bit pointers then the conversions are no-ops. -- Andreas Schwab, SUSE Labs, schwab@suse.de GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7 "And now for something completely different."