Messages in this thread Patch in this message |  | | Date | Sun, 21 Jan 2018 15:48:28 -0800 | From | Davidlohr Bueso <> | Subject | Re: [PATCH] arch/cris: use get_user_pages_fast() |
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On Sun, 21 Jan 2018, Al Viro wrote:
>On Sun, Jan 21, 2018 at 02:59:29PM -0800, Davidlohr Bueso wrote: >> Since we currently hold mmap_sem across both gup calls (and >> nothing more), we can substitute it with two _fast() >> alternatives and possibly avoid grabbing the lock. >> >> This was found while adding mmap_sem wrappers, and was also >> previously reported by Al: https://lkml.org/lkml/2017/11/17/777 > >See commit 9a949e8ff92246c0753b2805c2a001cb991fffe5 >Author: Al Viro <viro@zeniv.linux.org.uk> >Date: Sat Nov 18 14:37:46 2017 -0500 > > cris: switch to get_user_pages_fast() > > no point holding ->mmap_sem over both calls. > > Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Serves me for developing on Linus' tree, cool.
Now, regarding the other two which are technically bugs (not holding mmap_sem under gup), you mention I don't see those in next, so I'm assuming you didn't get to them.
- mthca_map_user_db(): I came to the same conclusion and tempted to send out the same idea of unlocking the mutex for gup_fast() so we can take mmap_sem if needed.
- ia64's store_virtual_to_phys() is a sysfs attribute and holds no (other) locks. How about we just convert it as well?
diff --git a/arch/ia64/kernel/err_inject.c b/arch/ia64/kernel/err_inject.c index 85bba43e7d5d..658a8e06a69b 100644 --- a/arch/ia64/kernel/err_inject.c +++ b/arch/ia64/kernel/err_inject.c @@ -142,7 +142,7 @@ store_virtual_to_phys(struct device *dev, struct device_attribute *attr, u64 virt_addr=simple_strtoull(buf, NULL, 16); int ret; - ret = get_user_pages(virt_addr, 1, FOLL_WRITE, NULL, NULL); + ret = get_user_pages_fast(virt_addr, 1, FOLL_WRITE, NULL); if (ret<=0) { #ifdef ERR_INJ_DEBUG printk("Virtual address %lx is not existing.\n",virt_addr);
Thanks, Davidlohr
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