#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/atomic.h>

/*
 * This is an implementation of the notion of "decrement a
 * reference count, and return locked if it decremented to zero".
 *
 * NOTE NOTE NOTE! This is _not_ equivalent to
 *
 *	if (atomic_dec_and_test(&atomic)) {
 *		spin_lock(&lock);
 *		return 1;
 *	}
 *	return 0;
 *
 * because the spin-lock and the decrement must be
 * "atomic".
 */
int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
{
	/* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
	if (atomic_add_unless(atomic, -1, 1))
		return 0;

	/* Otherwise do it the slow way */
	spin_lock(lock);
	if (atomic_dec_and_test(atomic))
		return 1;
	spin_unlock(lock);
	return 0;
}

EXPORT_SYMBOL(_atomic_dec_and_lock);
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<div class='path'>path: <a href='/cgit.cgi/linux/net-next.git/commit/?id=424414947da3dd5cb0d60e4f299f7c51e472ae77'>root</a>/<a href='/cgit.cgi/linux/net-next.git/commit/include?id=424414947da3dd5cb0d60e4f299f7c51e472ae77'>include</a>/<a href='/cgit.cgi/linux/net-next.git/commit/include/acpi?id=424414947da3dd5cb0d60e4f299f7c51e472ae77'>acpi</a>/<a href='/cgit.cgi/linux/net-next.git/commit/include/acpi/acpi.h?id=424414947da3dd5cb0d60e4f299f7c51e472ae77'>acpi.h</a></div><div class='content'><div class='cgit-panel'><b>diff options</b><form method='get'><input type='hidden' name='id' value='424414947da3dd5cb0d60e4f299f7c51e472ae77'/><table><tr><td colspan='2'/></tr><tr><td class='label'>context:</td><td class='ctrl'><select name='context' onchange='this.form.submit();'><option value='1'>1</option><option value='2'>2</option><option value='3' selected='selected'>3</option><option value='4'>4</option><option value='5'>5</option><option value='6'>6</option><option value='7'>7</option><option value='8'>8</option><option value='9'>9</option><option value='10'>10</option><option value='15'>15</option><option value='20'>20</option><option value='25'>25</option><option value='30'>30</option><option value='35'>35</option><option value='40'>40</option></select></td></tr><tr><td class='label'>space:</td><td class='ctrl'><select name='ignorews' onchange='this.form.submit();'><option value='0' selected='selected'>include</option><option value='1'>ignore</option></select></td></tr><tr><td class='label'>mode:</td><td class='ctrl'><select name='dt' onchange='this.form.submit();'><option value='0' selected='selected'>unified</option><option value='1'>ssdiff</option><option value='2'>stat only</option></select></td></tr><tr><td/><td class='ctrl'><noscript><input type='submit' value='reload'/></noscript></td></tr></table></form></div><table summary='commit info' class='commit-info'>
<tr><th>author</th><td>Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;</td><td class='right'>2017-02-03 22:19:15 +0100</td></tr>
<tr><th>committer</th><td>Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;</td><td class='right'>2017-02-03 22:19:15 +0100</td></tr>
<tr><th>commit</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/include/acpi/acpi.h?id=424414947da3dd5cb0d60e4f299f7c51e472ae77'>424414947da3dd5cb0d60e4f299f7c51e472ae77</a> (<a href='/cgit.cgi/linux/net-next.git/patch/include/acpi/acpi.h?id=424414947da3dd5cb0d60e4f299f7c51e472ae77'>patch</a>)</td></tr>
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<tr><th>parent</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/include/acpi/acpi.h?id=a3683e0c1410c5c8136a7a93b0336ce88d3b893a'>a3683e0c1410c5c8136a7a93b0336ce88d3b893a</a> (<a href='/cgit.cgi/linux/net-next.git/diff/include/acpi/acpi.h?id=424414947da3dd5cb0d60e4f299f7c51e472ae77&amp;id2=a3683e0c1410c5c8136a7a93b0336ce88d3b893a'>diff</a>)</td></tr><tr><th>parent</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/include/acpi/acpi.h?id=d07830db1bdb254e4b50d366010b219286b8c937'>d07830db1bdb254e4b50d366010b219286b8c937</a> (<a href='/cgit.cgi/linux/net-next.git/diff/include/acpi/acpi.h?id=424414947da3dd5cb0d60e4f299f7c51e472ae77&amp;id2=d07830db1bdb254e4b50d366010b219286b8c937'>diff</a>)</td></tr></table>
<div class='commit-subject'>Merge tag 'usb-serial-4.10-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/johan/usb-serial into usb-linus</div><div class='commit-msg'>Johan writes:

USB-serial fixes for v4.10-rc7

One more device ID for pl2303.

Signed-off-by: Johan Hovold &lt;johan@kernel.org&gt;
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