| Message ID | 1389948399-26344-1-git-send-email-m.szyprowski@samsung.com |
|---|---|
| State | New |
| Headers | show |
Hello, On 2014-01-17 11:49, Andy Whitcroft wrote: > On Fri, Jan 17, 2014 at 8:46 AM, Marek Szyprowski > <m.szyprowski@samsung.com> wrote: > > GFP_ATOMIC is not a single gfp flag, but a macro which expands to the other > > flags and LACK of __GFP_WAIT flag. To check if caller wanted to perform an > > atomic allocation, the code must test __GFP_WAIT flag presence. This patch > > fixes the issue introduced in v3.5-rc1 > > > > CC: stable@vger.kernel.org > > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> > > --- > > arch/x86/kernel/pci-dma.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c > > index 872079a..32a81c9 100644 > > --- a/arch/x86/kernel/pci-dma.c > > +++ b/arch/x86/kernel/pci-dma.c > > @@ -100,7 +100,7 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size, > > flag |= __GFP_ZERO; > > again: > > page = NULL; > > - if (!(flag & GFP_ATOMIC)) > > + if (flag & __GFP_WAIT) > > >From that description should this not actually be: > > if (!(flag & (GFP_ATOMIC|__GFP_WAIT) == GFP_ATOMIC)) > > Else we will start using this pool for more than __GFP_HIGH allocations? > > That said, it is possible this is right and the intent was to allow > __GFP_HIGH allocations (in general) to use this contigious pool, but I > will let someone more intimate with the code comment to that. I would > have hoped the code would have been as below in that case: > > if (!(flag & __GFP_HIGH)) > > Either way once this is resolved a nice comment should be added to > make it really clear: Exactly in this case, the GFP_ATOMIC check was (incorrectly) added by me in commit 0a2b9a6ea936 ("X86: integrate CMA with DMA-mapping subsystem"). My intention was to use CMA only if caller use other allocation flags than GFP_ATOMIC, because CMA cannot be used from atomic context. The pool is not aimed for __GFP_HIGH alocations. I will add additional comment to make clear why __GFP_WAIT flag is being checked. Best regards
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c index 872079a..32a81c9 100644 --- a/arch/x86/kernel/pci-dma.c +++ b/arch/x86/kernel/pci-dma.c @@ -100,7 +100,7 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size, flag |= __GFP_ZERO; again: page = NULL; - if (!(flag & GFP_ATOMIC)) + if (flag & __GFP_WAIT) page = dma_alloc_from_contiguous(dev, count, get_order(size)); if (!page) page = alloc_pages_node(dev_to_node(dev), flag, get_order(size));
GFP_ATOMIC is not a single gfp flag, but a macro which expands to the other flags and LACK of __GFP_WAIT flag. To check if caller wanted to perform an atomic allocation, the code must test __GFP_WAIT flag presence. This patch fixes the issue introduced in v3.5-rc1 CC: stable@vger.kernel.org Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> --- arch/x86/kernel/pci-dma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)