Re: [PATCH 1/1] kernel/fork.c: avoid division by zero
On 17.02.2015 08:56, Vladimir Davydov wrote: > On Mon, Feb 16, 2015 at 07:00:44PM +0100, Heinrich Schuchardt wrote: >> diff --git a/kernel/fork.c b/kernel/fork.c >> index cf65139..71e2583 100644 >> --- a/kernel/fork.c >> +++ b/kernel/fork.c >> @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages) >> * value: the thread structures can take up at most half >> * of memory. >> */ >> -max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); >> +max_threads = (u64) PAGE_SIZE * (u64) mempages >> +/ (u64) THREAD_SIZE / 8UL; > > This won't compile for a 32 bit arch, will it? Should you use div_u64? > > Thanks, > Vladimir > Hello Vladimir, I compiled the kernel successfully with the patch on a 32bit arm system and Kernel 3.19.0. Obviously that was good luck. http://gcc.gnu.org/onlinedocs/gccint/Integer-library-routines.html describes that library function __udivti3 might be used on other platforms. And using library functions is not allowable in the kernel. Thank you for reviewing. I will update the patch. Best regards Heinrich -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/1] kernel/fork.c: avoid division by zero
On 17.02.2015 08:56, Vladimir Davydov wrote: On Mon, Feb 16, 2015 at 07:00:44PM +0100, Heinrich Schuchardt wrote: diff --git a/kernel/fork.c b/kernel/fork.c index cf65139..71e2583 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages) * value: the thread structures can take up at most half * of memory. */ -max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); +max_threads = (u64) PAGE_SIZE * (u64) mempages +/ (u64) THREAD_SIZE / 8UL; This won't compile for a 32 bit arch, will it? Should you use div_u64? Thanks, Vladimir Hello Vladimir, I compiled the kernel successfully with the patch on a 32bit arm system and Kernel 3.19.0. Obviously that was good luck. http://gcc.gnu.org/onlinedocs/gccint/Integer-library-routines.html describes that library function __udivti3 might be used on other platforms. And using library functions is not allowable in the kernel. Thank you for reviewing. I will update the patch. Best regards Heinrich -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/1] kernel/fork.c: avoid division by zero
On Mon, Feb 16, 2015 at 07:00:44PM +0100, Heinrich Schuchardt wrote: > diff --git a/kernel/fork.c b/kernel/fork.c > index cf65139..71e2583 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages) >* value: the thread structures can take up at most half >* of memory. >*/ > - max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); > + max_threads = (u64) PAGE_SIZE * (u64) mempages > + / (u64) THREAD_SIZE / 8UL; This won't compile for a 32 bit arch, will it? Should you use div_u64? Thanks, Vladimir -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/1] kernel/fork.c: avoid division by zero
On 02/16/2015 10:45 AM, Heinrich Schuchardt wrote: I am resending this mail because the linux-kernel list was not CCed. Yes, sorry, that got lost. The "forward" feature on lkml.org doesn't work as well as it used to, unfortunately, and I keep forgetting. On 16.02.2015 19:23, Guenter Roeck wrote: On Mon, Feb 16, 2015 at 07:00:44PM +0100, Heinrich Schuchardt wrote: PAGE_SIZE is not guaranteed to be equal to or less than 8 times the THREAD_SIZE. E.g. architecture hexagon may have page size 1M and thread size 4096. This would lead to a division by zero. Signed-off-by: Heinrich Schuchardt --- kernel/fork.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index cf65139..71e2583 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages) * value: the thread structures can take up at most half * of memory. */ - max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); + max_threads = (u64) PAGE_SIZE * (u64) mempages + / (u64) THREAD_SIZE / 8UL; How about max_threads = mempages / (8 * THREAD_SIZE) * PAGE_SIZE; instead ? That would avoid the u64. We have to consider the case mempages < 8 * THREAD_SIZE. Let mempages = 1024 THREAD_SIZE = 4096 PAGE_SIZE = 1M Your code gives 0. Mine gives 8192. Makes sense. Thanks, Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/1] kernel/fork.c: avoid division by zero
I am resending this mail because the linux-kernel list was not CCed. On 16.02.2015 19:23, Guenter Roeck wrote: > On Mon, Feb 16, 2015 at 07:00:44PM +0100, Heinrich Schuchardt wrote: >> PAGE_SIZE is not guaranteed to be equal to or less than 8 times the >> THREAD_SIZE. >> >> E.g. architecture hexagon may have page size 1M and thread size 4096. >> >> This would lead to a division by zero. >> >> Signed-off-by: Heinrich Schuchardt >> --- >> kernel/fork.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/fork.c b/kernel/fork.c >> index cf65139..71e2583 100644 >> --- a/kernel/fork.c >> +++ b/kernel/fork.c >> @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages) >> * value: the thread structures can take up at most half >> * of memory. >> */ >> -max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); >> +max_threads = (u64) PAGE_SIZE * (u64) mempages >> +/ (u64) THREAD_SIZE / 8UL; > > How about > max_threads = mempages / (8 * THREAD_SIZE) * PAGE_SIZE; > > instead ? That would avoid the u64. We have to consider the case mempages < 8 * THREAD_SIZE. Let mempages = 1024 THREAD_SIZE = 4096 PAGE_SIZE = 1M Your code gives 0. Mine gives 8192. Best regards Heinrich -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH 1/1] kernel/fork.c: avoid division by zero
PAGE_SIZE is not guaranteed to be equal to or less than 8 times the THREAD_SIZE. E.g. architecture hexagon may have page size 1M and thread size 4096. This would lead to a division by zero. Signed-off-by: Heinrich Schuchardt --- kernel/fork.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index cf65139..71e2583 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages) * value: the thread structures can take up at most half * of memory. */ - max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); + max_threads = (u64) PAGE_SIZE * (u64) mempages + / (u64) THREAD_SIZE / 8UL; /* * we need to allow at least 20 threads to boot a system -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/1] kernel/fork.c: avoid division by zero
I am resending this mail because the linux-kernel list was not CCed. On 16.02.2015 19:23, Guenter Roeck wrote: On Mon, Feb 16, 2015 at 07:00:44PM +0100, Heinrich Schuchardt wrote: PAGE_SIZE is not guaranteed to be equal to or less than 8 times the THREAD_SIZE. E.g. architecture hexagon may have page size 1M and thread size 4096. This would lead to a division by zero. Signed-off-by: Heinrich Schuchardt xypron.g...@gmx.de --- kernel/fork.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index cf65139..71e2583 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages) * value: the thread structures can take up at most half * of memory. */ -max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); +max_threads = (u64) PAGE_SIZE * (u64) mempages +/ (u64) THREAD_SIZE / 8UL; How about max_threads = mempages / (8 * THREAD_SIZE) * PAGE_SIZE; instead ? That would avoid the u64. We have to consider the case mempages 8 * THREAD_SIZE. Let mempages = 1024 THREAD_SIZE = 4096 PAGE_SIZE = 1M Your code gives 0. Mine gives 8192. Best regards Heinrich -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/1] kernel/fork.c: avoid division by zero
On 02/16/2015 10:45 AM, Heinrich Schuchardt wrote: I am resending this mail because the linux-kernel list was not CCed. Yes, sorry, that got lost. The forward feature on lkml.org doesn't work as well as it used to, unfortunately, and I keep forgetting. On 16.02.2015 19:23, Guenter Roeck wrote: On Mon, Feb 16, 2015 at 07:00:44PM +0100, Heinrich Schuchardt wrote: PAGE_SIZE is not guaranteed to be equal to or less than 8 times the THREAD_SIZE. E.g. architecture hexagon may have page size 1M and thread size 4096. This would lead to a division by zero. Signed-off-by: Heinrich Schuchardt xypron.g...@gmx.de --- kernel/fork.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index cf65139..71e2583 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages) * value: the thread structures can take up at most half * of memory. */ - max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); + max_threads = (u64) PAGE_SIZE * (u64) mempages + / (u64) THREAD_SIZE / 8UL; How about max_threads = mempages / (8 * THREAD_SIZE) * PAGE_SIZE; instead ? That would avoid the u64. We have to consider the case mempages 8 * THREAD_SIZE. Let mempages = 1024 THREAD_SIZE = 4096 PAGE_SIZE = 1M Your code gives 0. Mine gives 8192. Makes sense. Thanks, Guenter -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH 1/1] kernel/fork.c: avoid division by zero
PAGE_SIZE is not guaranteed to be equal to or less than 8 times the THREAD_SIZE. E.g. architecture hexagon may have page size 1M and thread size 4096. This would lead to a division by zero. Signed-off-by: Heinrich Schuchardt xypron.g...@gmx.de --- kernel/fork.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index cf65139..71e2583 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages) * value: the thread structures can take up at most half * of memory. */ - max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); + max_threads = (u64) PAGE_SIZE * (u64) mempages + / (u64) THREAD_SIZE / 8UL; /* * we need to allow at least 20 threads to boot a system -- 2.1.4 -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/1] kernel/fork.c: avoid division by zero
On Mon, Feb 16, 2015 at 07:00:44PM +0100, Heinrich Schuchardt wrote: diff --git a/kernel/fork.c b/kernel/fork.c index cf65139..71e2583 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages) * value: the thread structures can take up at most half * of memory. */ - max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); + max_threads = (u64) PAGE_SIZE * (u64) mempages + / (u64) THREAD_SIZE / 8UL; This won't compile for a 32 bit arch, will it? Should you use div_u64? Thanks, Vladimir -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
