From: Keith Owens <kaos@sgi•com>
To: mita@miraclelinux•com (Akinobu Mita)
Cc: linux-mips@linux-mips•org, linux-ia64@vger•kernel.org,
Ian Molton <spyro@f2s•com>, Andi Kleen <ak@suse•de>,
David Howells <dhowells@redhat•com>,
linuxppc-dev@ozlabs•org, Greg Ungerer <gerg@uclinux•org>,
sparclinux@vger•kernel.org,
Miles Bader <uclinux-v850@lsi•nec.co.jp>,
Yoshinori Sato <ysato@users•sourceforge.jp>,
Hirokazu Takata <takata@linux-m32r•org>,
linuxsh-dev@lists•sourceforge.net,
Linus Torvalds <torvalds@osdl•org>,
Ivan Kokshaysky <ink@jurassic•park.msu.ru>,
Richard Henderson <rth@twiddle•net>,
Chris Zankel <chris@zankel•net>,
dev-etrax@axis•com, ultralinux@vger•kernel.org,
linux-m68k@lists•linux-m68k.org, linux-kernel@vger•kernel.org,
linuxsh-shmedia-dev@lists•sourceforge.net, linux390@de•ibm.com,
Russell King <rmk@arm•linux.org.uk>,
parisc-linux@parisc-linux•org
Subject: Re: [PATCH 3/6] C-language equivalents of include/asm-*/bitops.h
Date: Wed, 25 Jan 2006 22:54:43 +1100 [thread overview]
Message-ID: <24086.1138190083@ocs3.ocs.com.au> (raw)
In-Reply-To: Your message of "Wed, 25 Jan 2006 20:32:06 +0900." <20060125113206.GD18584@miraclelinux.com>
Akinobu Mita (on Wed, 25 Jan 2006 20:32:06 +0900) wrote:
>o generic {,test_and_}{set,clear,change}_bit() (atomic bitops)
...
>+static __inline__ void set_bit(int nr, volatile unsigned long *addr)
>+{
>+ unsigned long mask = BITOP_MASK(nr);
>+ unsigned long *p = ((unsigned long *)addr) + BITOP_WORD(nr);
>+ unsigned long flags;
>+
>+ _atomic_spin_lock_irqsave(p, flags);
>+ *p |= mask;
>+ _atomic_spin_unlock_irqrestore(p, flags);
>+}
Be very, very careful about using these generic *_bit() routines if the
architecture supports non-maskable interrupts.
NMI events can occur at any time, including when interrupts have been
disabled by *_irqsave(). So you can get NMI events occurring while a
*_bit fucntion is holding a spin lock. If the NMI handler also wants
to do bit manipulation (and they do) then you can get a deadlock
between the original caller of *_bit() and the NMI handler.
Doing any work that requires spinlocks in an NMI handler is just asking
for deadlock problems. The generic *_bit() routines add a hidden
spinlock behind what was previously a safe operation. I would even say
that any arch that supports any type of NMI event _must_ define its own
bit routines that do not rely on your _atomic_spin_lock_irqsave() and
its hash of spinlocks.
next prev parent reply other threads:[~2006-01-25 12:20 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-25 11:26 [PATCH 0/6] RFC: use include/asm-generic/bitops.h Akinobu Mita
2006-01-25 11:28 ` [PATCH 1/6] {set,clear,test}_bit() related cleanup Akinobu Mita
2006-01-26 16:14 ` Pavel Machek
2006-01-26 16:47 ` Russell King
2006-01-26 19:14 ` Paul Jackson
2006-01-25 11:30 ` [PATCH 2/6] use non atomic operations for minix_*_bit() and ext2_*_bit() Akinobu Mita
2006-01-25 11:32 ` [PATCH 3/6] C-language equivalents of include/asm-*/bitops.h Akinobu Mita
2006-01-25 11:54 ` Keith Owens [this message]
2006-01-26 2:13 ` Akinobu Mita
2006-01-25 20:02 ` Russell King
2006-01-25 23:25 ` Ian Molton
2006-01-26 0:06 ` Richard Henderson
2006-01-26 4:34 ` Edgar Toernig
2006-01-26 17:30 ` Richard Henderson
2006-01-26 8:55 ` Russell King
2006-01-26 16:18 ` [parisc-linux] " Grant Grundler
2006-01-26 16:30 ` Nicolas Pitre
2006-01-26 16:40 ` Russell King
2006-01-26 23:04 ` Grant Grundler
2006-01-26 23:03 ` Russell King
2006-01-29 7:12 ` Stuart Brady
2006-01-30 4:03 ` David S. Miller
2006-01-30 17:06 ` Ralf Baechle
2006-01-30 19:50 ` Stuart Brady
2006-01-30 23:02 ` David S. Miller
2006-01-27 0:28 ` [parisc-linux] Re: [PATCH 3/6] C-language equivalents of John David Anglin
2006-01-27 12:51 ` [PATCH 3/6] C-language equivalents of include/asm-*/bitops.h Hirokazu Takata
2006-01-30 3:29 ` Akinobu Mita
2006-01-25 11:34 ` [PATCH 5/6] fix warning on test_ti_thread_flag() Akinobu Mita
2006-01-25 12:28 ` Geert Uytterhoeven
2006-01-25 22:28 ` Paul Mackerras
2006-01-26 0:04 ` David S. Miller
2006-01-25 11:35 ` [PATCH 6/6] remove unused generic bitops in include/linux/bitops.h Akinobu Mita
[not found] ` <20060125113336.GE18584@miraclelinux.com>
2006-01-26 1:49 ` [PATCH 4/6] use include/asm-generic/bitops for each architecture Akinobu Mita
2006-01-27 13:04 ` Hirokazu Takata
2006-01-30 3:15 ` Akinobu Mita
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