Buildresult: linus/sun3_defconfig/m68k-gcc8 built on Oct 2 2020, 13:07

kisskb

Revisions | Branches | Compilers | Configs | Build Results | Build Failures |

Status:	OK
Date/Time:	Oct 2 2020, 13:07
Duration:	0:02:30.014057
Builder:	blade4b
Revision:	pipe: remove pipe_wait() and fix wakeup race with splice (`472e5b056f000a778abb41f1e443de58eb259783)`
Target:	linus/sun3_defconfig/m68k-gcc8
Branch:	linus
Compiler:	m68k-gcc8 (m68k-linux-gcc (GCC) 8.1.0 / GNU ld (GNU Binutils) 2.30)
Config:	sun3_defconfig (download)
Log:	Download original Possible warnings (5) WARNING: unmet direct dependencies detected for NEED_MULTIPLE_NODES WARNING: unmet direct dependencies detected for NEED_MULTIPLE_NODES WARNING: unmet direct dependencies detected for NEED_MULTIPLE_NODES WARNING: unmet direct dependencies detected for NEED_MULTIPLE_NODES arch/m68k/include/asm/cmpxchg.h:79:22: warning: value computed is not used [-Wunused-value] Full Log # git rev-parse -q --verify 472e5b056f000a778abb41f1e443de58eb259783^{commit} 472e5b056f000a778abb41f1e443de58eb259783 already have revision, skipping fetch # git checkout -q -f -B kisskb 472e5b056f000a778abb41f1e443de58eb259783 # git clean -qxdf # < git log -1 # commit 472e5b056f000a778abb41f1e443de58eb259783 # Author: Linus Torvalds <torvalds@linux-foundation.org> # Date: Thu Oct 1 19:14:36 2020 -0700 # # pipe: remove pipe_wait() and fix wakeup race with splice # # The pipe splice code still used the old model of waiting for pipe IO by # using a non-specific "pipe_wait()" that waited for any pipe event to # happen, which depended on all pipe IO being entirely serialized by the # pipe lock. So by checking the state you were waiting for, and then # adding yourself to the wait queue before dropping the lock, you were # guaranteed to see all the wakeups. # # Strictly speaking, the actual wakeups were not done under the lock, but # the pipe_wait() model still worked, because since the waiter held the # lock when checking whether it should sleep, it would always see the # current state, and the wakeup was always done after updating the state. # # However, commit 0ddad21d3e99 ("pipe: use exclusive waits when reading or # writing") split the single wait-queue into two, and in the process also # made the "wait for event" code wait for _two_ wait queues, and that then # showed a race with the wakers that were not serialized by the pipe lock. # # It's only splice that used that "pipe_wait()" model, so the problem # wasn't obvious, but Josef Bacik reports: # # "I hit a hang with fstest btrfs/187, which does a btrfs send into # /dev/null. This works by creating a pipe, the write side is given to # the kernel to write into, and the read side is handed to a thread that # splices into a file, in this case /dev/null. # # The box that was hung had the write side stuck here [pipe_write] and # the read side stuck here [splice_from_pipe_next -> pipe_wait]. # # [ more details about pipe_wait() scenario ] # # The problem is we're doing the prepare_to_wait, which sets our state # each time, however we can be woken up either with reads or writes. In # the case above we race with the WRITER waking us up, and re-set our # state to INTERRUPTIBLE, and thus never break out of schedule" # # Josef had a patch that avoided the issue in pipe_wait() by just making # it set the state only once, but the deeper problem is that pipe_wait() # depends on a level of synchonization by the pipe mutex that it really # shouldn't. And the whole "wait for any pipe state change" model really # isn't very good to begin with. # # So rather than trying to work around things in pipe_wait(), remove that # legacy model of "wait for arbitrary pipe event" entirely, and actually # create functions that wait for the pipe actually being readable or # writable, and can do so without depending on the pipe lock serializing # everything. # # Fixes: 0ddad21d3e99 ("pipe: use exclusive waits when reading or writing") # Link: https://lore.kernel.org/linux-fsdevel/bfa88b5ad6f069b2b679316b9e495a970130416c.1601567868.git.josef@toxicpanda.com/ # Reported-by: Josef Bacik <josef@toxicpanda.com> # Reviewed-and-tested-by: Josef Bacik <josef@toxicpanda.com> # Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/m68k-linux/bin/m68k-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/m68k-linux/bin/m68k-linux-ld --version # < git log --format=%s --max-count=1 472e5b056f000a778abb41f1e443de58eb259783 # < make -s -j 24 ARCH=m68k O=/kisskb/build/linus_sun3_defconfig_m68k-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/m68k-linux/bin/m68k-linux- sun3_defconfig WARNING: unmet direct dependencies detected for NEED_MULTIPLE_NODES Depends on [n]: DISCONTIGMEM [=n] \|\| NUMA Selected by [y]: - SINGLE_MEMORY_CHUNK [=y] && MMU [=y] WARNING: unmet direct dependencies detected for NEED_MULTIPLE_NODES Depends on [n]: DISCONTIGMEM [=n] \|\| NUMA Selected by [y]: - SINGLE_MEMORY_CHUNK [=y] && MMU [=y] # < make -s -j 24 ARCH=m68k O=/kisskb/build/linus_sun3_defconfig_m68k-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/m68k-linux/bin/m68k-linux- help # make -s -j 24 ARCH=m68k O=/kisskb/build/linus_sun3_defconfig_m68k-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/m68k-linux/bin/m68k-linux- olddefconfig WARNING: unmet direct dependencies detected for NEED_MULTIPLE_NODES Depends on [n]: DISCONTIGMEM [=n] \|\| NUMA Selected by [y]: - SINGLE_MEMORY_CHUNK [=y] && MMU [=y] WARNING: unmet direct dependencies detected for NEED_MULTIPLE_NODES Depends on [n]: DISCONTIGMEM [=n] \|\| NUMA Selected by [y]: - SINGLE_MEMORY_CHUNK [=y] && MMU [=y] # make -s -j 24 ARCH=m68k O=/kisskb/build/linus_sun3_defconfig_m68k-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/m68k-linux/bin/m68k-linux- In file included from /kisskb/src/arch/m68k/include/asm/atomic.h:7, from /kisskb/src/include/linux/atomic.h:7, from /kisskb/src/include/linux/cpumask.h:13, from /kisskb/src/include/linux/smp.h:13, from /kisskb/src/include/linux/lockdep.h:14, from /kisskb/src/include/linux/spinlock.h:59, from /kisskb/src/include/linux/wait.h:9, from /kisskb/src/include/linux/wait_bit.h:8, from /kisskb/src/include/linux/fs.h:6, from /kisskb/src/fs/ocfs2/file.c:13: /kisskb/src/fs/ocfs2/file.c: In function 'ocfs2_file_write_iter': /kisskb/src/arch/m68k/include/asm/cmpxchg.h:79:22: warning: value computed is not used [-Wunused-value] #define xchg(ptr,x) ((__typeof__((ptr)))__xchg((unsigned long)(x),(ptr),sizeof((ptr)))) ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /kisskb/src/fs/ocfs2/file.c:2419:3: note: in expansion of macro 'xchg' xchg(&iocb->ki_complete, saved_ki_complete); ^~~~ Completed OK # rm -rf /kisskb/build/linus_sun3_defconfig_m68k-gcc8 # Build took: 0:02:30.014057

© Michael Ellerman 2006-2018.