On Wed, Nov 14, 2018 at 03:43:05PM +0100, Christophe LEROY wrote: > > > Le 09/11/2018 à 21:10, Paul E. McKenney a écrit : > >On Fri, Nov 09, 2018 at 06:11:20PM +0100, Christophe LEROY wrote: > >>(Resending due to error in Paul's address) > >> > >>Paul > >> > >>I get the following UBSAN reports in 4.20-rc1 on an MPC8321E > >>(powerpc/book3s/32) > >> > >>I bisected it to 3e31009898699dfc ("rcu: Defer reporting RCU-preempt > >>quiescent states when disabled") > > > >Fixed by dfdc33585b0a ("rcu: Avoid signed integer overflow in > >rcu_preempt_deferred_qs()") in my -rcu tree and in -next, which I intend > >to push into the next merge window. > > Thanks, I confirm it fixes the issue. > > Do you intend to push it into 4.20-rc3 or do you mean 4.21 ?
The next merge window, which will be either v4.21 or v5.0. The v4.20 merge window is over and done. ;-) Please note that the gcc command-line arguments used by the Linux kernel prevent the compiler from taking advantage of the C-standard signed integer overflow aspect of undefined behavior, so this is a aesthetic issue rather than a failure case. Plus the C++ standards committee just voted in a change that gets rid of signed integer overflow completely. It is not clear whether the C language will also make this change, but it does require that the usual compilers have the ability to operate in this manner. Thanx, Paul > Christophe > > > Thanx, Paul > > > >>Thanks > >>Christophe > >> > >>[ 4.919995] > >>================================================================================ > >>[ 4.928428] UBSAN: Undefined behaviour in kernel/rcu/tree_plugin.h:623:28 > >>[ 4.935198] signed integer overflow: > >>[ 4.938766] 0 - -2147483648 cannot be represented in type 'int' > >>[ 4.944678] CPU: 0 PID: 119 Comm: mkdir Not tainted > >>4.19.0-rc1-s3k-dev-00005-g5a60513 #214 > >>[ 4.952908] Call Trace: > >>[ 4.955382] [dec4fd20] [c02cb0d0] ubsan_epilogue+0x18/0x74 (unreliable) > >>[ 4.962003] [dec4fd30] [c02cb5e0] handle_overflow+0xd0/0xe0 > >>[ 4.967588] [dec4fdb0] [c007b424] rcu_preempt_deferred_qs+0xc0/0xc8 > >>[ 4.973857] [dec4fdd0] [c007be28] rcu_note_context_switch+0x74/0x608 > >>[ 4.980217] [dec4fe10] [c064b790] __schedule+0x58/0x6e0 > >>[ 4.985448] [dec4fe50] [c064bfdc] preempt_schedule_common+0x48/0x9c > >>[ 4.991717] [dec4fe70] [c01308c8] handle_mm_fault+0x10fc/0x1ecc > >>[ 4.997639] [dec4fee0] [c001339c] do_page_fault+0x10c/0x760 > >>[ 5.003225] [dec4ff40] [c001234c] handle_page_fault+0x14/0x40 > >>[ 5.008968] --- interrupt: 401 at 0xff9cff8 > >>[ 5.008968] LR = 0xfeefd78 > >>[ 5.016170] > >>================================================================================ > >>[ 5.024591] > >>================================================================================ > >>[ 5.033005] UBSAN: Undefined behaviour in kernel/rcu/tree_plugin.h:627:28 > >>[ 5.039775] signed integer overflow: > >>[ 5.043342] -2147483648 + -2147483648 cannot be represented in type 'int' > >>[ 5.050118] CPU: 0 PID: 119 Comm: mkdir Not tainted > >>4.19.0-rc1-s3k-dev-00005-g5a60513 #214 > >>[ 5.058348] Call Trace: > >>[ 5.060813] [dec4fd20] [c02cb0d0] ubsan_epilogue+0x18/0x74 (unreliable) > >>[ 5.067433] [dec4fd30] [c02cb5e0] handle_overflow+0xd0/0xe0 > >>[ 5.073014] [dec4fdb0] [c007b408] rcu_preempt_deferred_qs+0xa4/0xc8 > >>[ 5.079283] [dec4fdd0] [c007be28] rcu_note_context_switch+0x74/0x608 > >>[ 5.085640] [dec4fe10] [c064b790] __schedule+0x58/0x6e0 > >>[ 5.090871] [dec4fe50] [c064bfdc] preempt_schedule_common+0x48/0x9c > >>[ 5.097139] [dec4fe70] [c01308c8] handle_mm_fault+0x10fc/0x1ecc > >>[ 5.103059] [dec4fee0] [c001339c] do_page_fault+0x10c/0x760 > >>[ 5.108642] [dec4ff40] [c001234c] handle_page_fault+0x14/0x40 > >>[ 5.114385] --- interrupt: 401 at 0xff9cff8 > >>[ 5.114385] LR = 0xfeefd78 > >>[ 5.121588] > >>================================================================================ > >> >