On 2019-12-18 11:24 a.m., Bjorn Helgaas wrote: > On Wed, Dec 18, 2019 at 12:00:04PM -0500, Qian Cai wrote: >> The commit a7d06153eea2 ("PCI: Fix pci_add_dma_alias() bitmask size") >> introduced a compilation warning and a potential infinite loop because >> it is no longer possible to be self-terminated as u8 is always less than >> 256, >> >> In file included from ./include/linux/kernel.h:12, >> from ./include/asm-generic/bug.h:19, >> from ./arch/x86/include/asm/bug.h:83, >> from ./include/linux/bug.h:5, >> from ./include/linux/jump_label.h:250, >> from ./arch/x86/include/asm/string_64.h:6, >> from ./arch/x86/include/asm/string.h:5, >> from ./include/linux/string.h:20, >> from ./include/linux/uuid.h:12, >> from ./include/linux/mod_devicetable.h:13, >> from ./include/linux/pci.h:27, >> from drivers/pci/search.c:11: >> drivers/pci/search.c: In function 'pci_for_each_dma_alias': >> ./include/linux/bitops.h:30:13: warning: comparison is always true due >> to limited range of data type [-Wtype-limits] >> (bit) < (size); \ >> ^ >> drivers/pci/search.c:46:3: note: in expansion of macro 'for_each_set_bit' >> for_each_set_bit(devfn, pdev->dma_alias_mask, MAX_NR_DEVFNS) { >> >> Fixed it by using u16 for "devfn" in this occasion. > > Ugh, that is pretty subtle! Would you mind if we used "unsigned int" > instead of "u16"? "u16" makes it look like just a mistake -- somebody > is likely to come along and say devfn only needs "u8" and try to > change it back. The same might happen with "unsigned int", but at > least it doesn't look like it was chosen specifically to fit a devfn. I agree: you're right that we really don't need an int that's specifically sized here. There's really shouldn't be any gain in using a smaller integer, in theory "int" should be the most "efficient" anyway, just using a full register in hardware. Logan > Provisional patch below. > >> Fixes: a7d06153eea2 ("PCI: Fix pci_add_dma_alias() bitmask size") >> Signed-off-by: Qian Cai <cai@xxxxxx> >> --- >> drivers/pci/search.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/pci/search.c b/drivers/pci/search.c >> index 9e4dfae47252..42bc44d0e681 100644 >> --- a/drivers/pci/search.c >> +++ b/drivers/pci/search.c >> @@ -41,7 +41,7 @@ int pci_for_each_dma_alias(struct pci_dev *pdev, >> * DMA, iterate over that too. >> */ >> if (unlikely(pdev->dma_alias_mask)) { >> - u8 devfn; >> + u16 devfn; >> >> for_each_set_bit(devfn, pdev->dma_alias_mask, MAX_NR_DEVFNS) { >> ret = fn(pdev, PCI_DEVID(pdev->bus->number, devfn), >> -- >> 2.21.0 (Apple Git-122.2) > > commit f8bf2aeb651b ("PCI: Fix pci_add_dma_alias() bitmask size") > Author: James Sewart <jamessewart@xxxxxxxxxx> > Date: Tue Dec 10 15:51:33 2019 -0600 > > PCI: Fix pci_add_dma_alias() bitmask size > > The number of possible devfns is 256, but pci_add_dma_alias() allocated a > bitmap of size 255. Fix this off-by-one error. > > This fixes commits 338c3149a221 ("PCI: Add support for multiple DMA > aliases") and c6635792737b ("PCI: Allocate dma_alias_mask with > bitmap_zalloc()"), but I doubt it was possible to see a problem because > it takes 4 64-bit longs (or 8 32-bit longs) to hold 255 bits, and > bitmap_zalloc() doesn't save the 255-bit size anywhere. > > [bhelgaas: commit log, move #define to drivers/pci/pci.h, include loop > limit fix from Qian Cai: > https://lore.kernel.org/r/20191218170004.5297-1-cai@xxxxxx] > Signed-off-by: James Sewart <jamessewart@xxxxxxxxxx> > Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx> > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > index e87196cc1a7f..7b5fa2eabe09 100644 > --- a/drivers/pci/pci.c > +++ b/drivers/pci/pci.c > @@ -6017,7 +6017,7 @@ EXPORT_SYMBOL_GPL(pci_pr3_present); > void pci_add_dma_alias(struct pci_dev *dev, u8 devfn) > { > if (!dev->dma_alias_mask) > - dev->dma_alias_mask = bitmap_zalloc(U8_MAX, GFP_KERNEL); > + dev->dma_alias_mask = bitmap_zalloc(MAX_NR_DEVFNS, GFP_KERNEL); > if (!dev->dma_alias_mask) { > pci_warn(dev, "Unable to allocate DMA alias mask\n"); > return; > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h > index a0a53bd05a0b..6394e7746fb5 100644 > --- a/drivers/pci/pci.h > +++ b/drivers/pci/pci.h > @@ -4,6 +4,9 @@ > > #include <linux/pci.h> > > +/* Number of possible devfns: 0.0 to 1f.7 inclusive */ > +#define MAX_NR_DEVFNS 256 > + > #define PCI_FIND_CAP_TTL 48 > > #define PCI_VSEC_ID_INTEL_TBT 0x1234 /* Thunderbolt */ > diff --git a/drivers/pci/search.c b/drivers/pci/search.c > index bade14002fd8..e4dbdef5aef0 100644 > --- a/drivers/pci/search.c > +++ b/drivers/pci/search.c > @@ -41,9 +41,9 @@ int pci_for_each_dma_alias(struct pci_dev *pdev, > * DMA, iterate over that too. > */ > if (unlikely(pdev->dma_alias_mask)) { > - u8 devfn; > + unsigned int devfn; > > - for_each_set_bit(devfn, pdev->dma_alias_mask, U8_MAX) { > + for_each_set_bit(devfn, pdev->dma_alias_mask, MAX_NR_DEVFNS) { > ret = fn(pdev, PCI_DEVID(pdev->bus->number, devfn), > data); > if (ret) >