Messages in this thread | | | From | "Luck, Tony" <> | Subject | RE: [PATCH v2 2/6] bitops: always define asm-generic non-atomic bitops | Date | Fri, 10 Jun 2022 16:02:03 +0000 |
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> > +/** > > + * generic_test_bit - Determine whether a bit is set > > + * @nr: bit number to test > > + * @addr: Address to start counting from > > + */ > > Shouldn't we add in this or in separate patch a big NOTE to explain that this > is actually atomic and must be kept as a such?
"atomic" isn't really the right word. The volatile access makes sure that the compiler does the test at the point that the source code asked, and doesn't move it before/after other operations.
But there is no such thing as an atomic test_bit() operation:
if (test_bit(5, addr)) { /* some other CPU nukes bit 5 */
/* I know it was set when I looked, but now, could be anything */
... }
-Tony
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