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Date: Mon, 12 Jan 2015 15:19:11 +0100 From: David Hildenbrand <dahi@...ux.vnet.ibm.com> To: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, tglx@...utronix.de, peterz@...radead.org Cc: benh@...nel.crashing.org, paulus@...ba.org, akpm@...ux-foundation.org, heiko.carstens@...ibm.com, schwidefsky@...ibm.com, borntraeger@...ibm.com, mst@...hat.com, David.Laight@...LAB.COM, hughd@...gle.com, hocko@...e.cz Subject: Re: [PATCH v2 0/5] Reenable might_sleep() checks for might_fault() Thomas, Peter, anything that speaks against putting the pagefault_disable counter into thread_info (my series) instead of task_struct (rt tree)? IOW, what would be the right place for it? Would be good to know for me how to proceed with this series. Thanks! David > v1 -> v2: > - moved pagefault_count to the end of thread_info for all archs that would have > required manually calculating asm-offsets - to keep changes minimal. > - remove unlikely() from "mm, uaccess: trigger might_sleep() in" and keep > changes minimal (in_atomic() -> pagefault_disabled()) > > ---- > > I recently discovered that might_fault() doesn't call might_sleep() anymore. > Therefore bugs like: > spin_lock(&lock); > rc = copy_to_user(...); > spin_unlock(&lock); > would not be detected with CONFIG_DEBUG_ATOMIC_SLEEP. The code was changed to > disable false positives for code like: > pagefault_disable(); > rc = copy_to_user(...); > pagefault_enable(); > > Until now, pagefault_disable() and pagefault_enable() simply modified the > preempt count, therefore telling the pagefault handler that the context is > atomic and sleeping is disallowed. > > In order to reenable might_sleep() checks for the correct path, we need a way to > detect whether we run in a pagefault_disable() context. > > This series therefore introduces a separate pagefault_count and uses it to count > the levels of pagefault_disable() per thread. might_sleep() checks are > reactivated for the !pagefault_disable() path. > > So this should now work: > spin_lock(&lock); /* also if left away */ > pagefault_disable() > rc = copy_to_user(...); > pagefault_enable(); > spin_unlock(&lock); > And this should report a warning again: > spin_lock(&lock); > rc = copy_to_user(...); > spin_unlock(&lock); > > Please note that this series will not completely split the handling of > pagefault_disable() and the preempt count. This will be done in another series. > Purpose of this series is to reenable might_sleep() checks for might_fault(), > avoiding to produce false positives. > > Cross compiled on powerpc, arm, sparc, sparc64, arm64, x86_64, i386, mips, > alpha, ia64, xtensa, m68k, microblaze. > > Tested on s390. > > > David Hildenbrand (5): > uaccess: add pagefault_count to thread_info > uaccess: count pagefault_disable() levels in pagefault_count > mm, uaccess: trigger might_sleep() in might_fault() when pagefaults > are disabled > uaccess: clarify that uaccess may only sleep if pagefaults are not > disabled > uaccess: CONFIG_DEBUG_PAGEFAULT_COUNT to debug pagefault_count > > arch/alpha/include/asm/thread_info.h | 1 + > arch/arc/include/asm/thread_info.h | 1 + > arch/arm/include/asm/thread_info.h | 1 + > arch/arm64/include/asm/thread_info.h | 1 + > arch/avr32/include/asm/thread_info.h | 1 + > arch/avr32/include/asm/uaccess.h | 12 +++++--- > arch/blackfin/include/asm/thread_info.h | 1 + > arch/c6x/include/asm/thread_info.h | 1 + > arch/cris/include/asm/thread_info.h | 1 + > arch/frv/include/asm/thread_info.h | 1 + > arch/hexagon/include/asm/thread_info.h | 1 + > arch/hexagon/include/asm/uaccess.h | 3 +- > arch/ia64/include/asm/thread_info.h | 1 + > arch/m32r/include/asm/thread_info.h | 1 + > arch/m32r/include/asm/uaccess.h | 30 ++++++++++++------ > arch/m68k/include/asm/thread_info.h | 1 + > arch/metag/include/asm/thread_info.h | 1 + > arch/microblaze/include/asm/thread_info.h | 1 + > arch/microblaze/include/asm/uaccess.h | 6 ++-- > arch/mips/include/asm/thread_info.h | 1 + > arch/mips/include/asm/uaccess.h | 45 ++++++++++++++++++--------- > arch/mn10300/include/asm/thread_info.h | 1 + > arch/openrisc/include/asm/thread_info.h | 1 + > arch/parisc/include/asm/thread_info.h | 1 + > arch/powerpc/include/asm/thread_info.h | 1 + > arch/s390/include/asm/thread_info.h | 1 + > arch/s390/include/asm/uaccess.h | 15 ++++++--- > arch/score/include/asm/thread_info.h | 1 + > arch/score/include/asm/uaccess.h | 15 ++++++--- > arch/sh/include/asm/thread_info.h | 1 + > arch/sparc/include/asm/thread_info_32.h | 1 + > arch/sparc/include/asm/thread_info_64.h | 1 + > arch/tile/include/asm/thread_info.h | 1 + > arch/tile/include/asm/uaccess.h | 21 ++++++++----- > arch/um/include/asm/thread_info.h | 1 + > arch/unicore32/include/asm/thread_info.h | 1 + > arch/x86/include/asm/thread_info.h | 1 + > arch/x86/include/asm/uaccess.h | 15 ++++++--- > arch/x86/include/asm/uaccess_32.h | 6 ++-- > arch/x86/lib/usercopy_32.c | 6 ++-- > arch/xtensa/include/asm/thread_info.h | 1 + > include/linux/kernel.h | 3 +- > include/linux/uaccess.h | 51 ++++++++++++++++++++++++++----- > lib/Kconfig.debug | 9 ++++++ > lib/strnlen_user.c | 6 ++-- > mm/maccess.c | 11 +++++++ > mm/memory.c | 18 ++++------- > 47 files changed, 222 insertions(+), 80 deletions(-) > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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