# git rev-parse -q --verify 3a34b13a88caeb2800ab44a4918f230041b37dd9^{commit}
3a34b13a88caeb2800ab44a4918f230041b37dd9
already have revision, skipping fetch
# git checkout -q -f -B kisskb 3a34b13a88caeb2800ab44a4918f230041b37dd9
# git clean -qxdf
# < git log -1
# commit 3a34b13a88caeb2800ab44a4918f230041b37dd9
# Author: Linus Torvalds <torvalds@linux-foundation.org>
# Date:   Fri Jul 30 15:42:34 2021 -0700
# 
#     pipe: make pipe writes always wake up readers
#     
#     Since commit 1b6b26ae7053 ("pipe: fix and clarify pipe write wakeup
#     logic") we have sanitized the pipe write logic, and would only try to
#     wake up readers if they needed it.
#     
#     In particular, if the pipe already had data in it before the write,
#     there was no point in trying to wake up a reader, since any existing
#     readers must have been aware of the pre-existing data already.  Doing
#     extraneous wakeups will only cause potential thundering herd problems.
#     
#     However, it turns out that some Android libraries have misused the EPOLL
#     interface, and expected "edge triggered" be to "any new write will
#     trigger it".  Even if there was no edge in sight.
#     
#     Quoting Sandeep Patil:
#      "The commit 1b6b26ae7053 ('pipe: fix and clarify pipe write wakeup
#       logic') changed pipe write logic to wakeup readers only if the pipe
#       was empty at the time of write. However, there are libraries that
#       relied upon the older behavior for notification scheme similar to
#       what's described in [1]
#     
#       One such library 'realm-core'[2] is used by numerous Android
#       applications. The library uses a similar notification mechanism as GNU
#       Make but it never drains the pipe until it is full. When Android moved
#       to v5.10 kernel, all applications using this library stopped working.
#     
#       The library has since been fixed[3] but it will be a while before all
#       applications incorporate the updated library"
#     
#     Our regression rule for the kernel is that if applications break from
#     new behavior, it's a regression, even if it was because the application
#     did something patently wrong.  Also note the original report [4] by
#     Michal Kerrisk about a test for this epoll behavior - but at that point
#     we didn't know of any actual broken use case.
#     
#     So add the extraneous wakeup, to approximate the old behavior.
#     
#     [ I say "approximate", because the exact old behavior was to do a wakeup
#       not for each write(), but for each pipe buffer chunk that was filled
#       in. The behavior introduced by this change is not that - this is just
#       "every write will cause a wakeup, whether necessary or not", which
#       seems to be sufficient for the broken library use. ]
#     
#     It's worth noting that this adds the extraneous wakeup only for the
#     write side, while the read side still considers the "edge" to be purely
#     about reading enough from the pipe to allow further writes.
#     
#     See commit f467a6a66419 ("pipe: fix and clarify pipe read wakeup logic")
#     for the pipe read case, which remains that "only wake up if the pipe was
#     full, and we read something from it".
#     
#     Link: https://lore.kernel.org/lkml/CAHk-=wjeG0q1vgzu4iJhW5juPkTsjTYmiqiMUYAebWW+0bam6w@mail.gmail.com/ [1]
#     Link: https://github.com/realm/realm-core [2]
#     Link: https://github.com/realm/realm-core/issues/4666 [3]
#     Link: https://lore.kernel.org/lkml/CAKgNAkjMBGeAwF=2MKK758BhxvW58wYTgYKB2V-gY1PwXxrH+Q@mail.gmail.com/ [4]
#     Link: https://lore.kernel.org/lkml/20210729222635.2937453-1-sspatil@android.com/
#     Reported-by: Sandeep Patil <sspatil@android.com>
#     Cc: Michael Kerrisk <mtk.manpages@gmail.com>
#     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
# < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/hppa-linux/bin/hppa-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/hppa-linux/bin/hppa-linux-ld --version
# < git log --format=%s --max-count=1 3a34b13a88caeb2800ab44a4918f230041b37dd9
# < make -s -j 48 ARCH=parisc O=/kisskb/build/linus_generic-32bit_defconfig_parisc-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/hppa-linux/bin/hppa-linux-  generic-32bit_defconfig
# < make -s -j 48 ARCH=parisc O=/kisskb/build/linus_generic-32bit_defconfig_parisc-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/hppa-linux/bin/hppa-linux-  help
# make -s -j 48 ARCH=parisc O=/kisskb/build/linus_generic-32bit_defconfig_parisc-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/hppa-linux/bin/hppa-linux-  olddefconfig
# make -s -j 48 ARCH=parisc O=/kisskb/build/linus_generic-32bit_defconfig_parisc-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/hppa-linux/bin/hppa-linux-  
/kisskb/src/arch/parisc/math-emu/fpudispatch.c: In function 'decode_0c':
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:312:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+2] = fpregs[r1+2];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:313:9: note: here
         case 1: /* double */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:314:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+1] = fpregs[r1+1];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:315:9: note: here
         case 0: /* single */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:327:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+2] = fpregs[r1+2];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:328:9: note: here
         case 1: /* double */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:329:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+1] = fpregs[r1+1];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:330:9: note: here
         case 0: /* single */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:343:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+2] = fpregs[r1+2];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:344:9: note: here
         case 1: /* double */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:345:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+1] = fpregs[r1+1];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:346:9: note: here
         case 0: /* single */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:359:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+2] = fpregs[r1+2];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:360:9: note: here
         case 1: /* double */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:361:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+1] = fpregs[r1+1];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:362:9: note: here
         case 0: /* single */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:305:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:319:4: note: here
    case 3: /* FABS */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:320:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:335:4: note: here
    case 6: /* FNEG */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:336:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:351:4: note: here
    case 7: /* FNEGABS */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:352:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:367:4: note: here
    case 4: /* FSQRT */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:368:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:379:4: note: here
    case 5: /* FRND */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:410:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:422:4: note: here
    case 1: /* FCNVXF */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:423:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:437:4: note: here
    case 2: /* FCNVFX */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:438:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:452:4: note: here
    case 3: /* FCNVFXT */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:453:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:467:4: note: here
    case 5: /* FCNVUF (PA2.0 only) */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:468:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:482:4: note: here
    case 6: /* FCNVFU (PA2.0 only) */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:483:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:497:4: note: here
    case 7: /* FCNVFUT (PA2.0 only) */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:498:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:512:4: note: here
    case 4: /* undefined */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:574:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:593:4: note: here
    case 1: /* FTEST */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:625:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:636:4: note: here
    case 1: /* FSUB */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:637:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:648:4: note: here
    case 2: /* FMPY */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:649:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:660:4: note: here
    case 3: /* FDIV */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:661:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:672:4: note: here
    case 4: /* FREM */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:300:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   switch (subop) {
   ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:393:2: note: here
  case 1: /* class 1 */
  ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:408:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   switch (subop) {
   ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:516:2: note: here
  case 2: /* class 2 */
  ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:521:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
   if  (fpu_type_flags & PA2_0_FPU_FLAG) {
       ^
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:614:2: note: here
  case 3: /* class 3 */
  ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c: In function 'decode_0e':
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:738:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+1] = fpregs[r1+1];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:739:9: note: here
         case 0: /* single */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:749:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+1] = fpregs[r1+1];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:750:9: note: here
         case 0: /* single */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:760:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+1] = fpregs[r1+1];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:761:9: note: here
         case 0: /* single */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:771:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
      fpregs[t+1] = fpregs[r1+1];
      ~~~~~~~~~~~~^~~~~~~~~~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:772:9: note: here
         case 0: /* single */
         ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:733:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:743:4: note: here
    case 3: /* FABS */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:744:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:754:4: note: here
    case 6: /* FNEG */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:755:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:765:4: note: here
    case 7: /* FNEGABS */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:766:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:776:4: note: here
    case 4: /* FSQRT */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:777:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:788:4: note: here
    case 5: /* FRMD */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:817:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:829:4: note: here
    case 1: /* FCNVXF */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:830:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:844:4: note: here
    case 2: /* FCNVFX */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:845:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:859:4: note: here
    case 3: /* FCNVFXT */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:860:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:874:4: note: here
    case 5: /* FCNVUF (PA2.0 only) */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:875:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:889:4: note: here
    case 6: /* FCNVFU (PA2.0 only) */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:890:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:904:4: note: here
    case 7: /* FCNVFUT (PA2.0 only) */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:905:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch(fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:919:4: note: here
    case 4: /* undefined */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:1021:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:1029:4: note: here
    case 1: /* FSUB */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:1030:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:1038:4: note: here
    case 2: /* FMPY or XMPYU */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:1042:8: warning: this statement may fall through [-Wimplicit-fallthrough=]
     if (extru(ir,fpxpos,1)) {
        ^
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:1074:4: note: here
    case 3: /* FDIV */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:1075:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     switch (fmt) {
     ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:1083:4: note: here
    case 4: /* FREM */
    ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:728:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   switch (subop) {
   ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:802:2: note: here
  case 1: /* class 1 */
  ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:815:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   switch (subop) {
   ^~~~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:922:2: note: here
  case 2: /* class 2 */
  ^~~~
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:938:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
   if  (fpu_type_flags & PA2_0_FPU_FLAG) {
       ^
/kisskb/src/arch/parisc/math-emu/fpudispatch.c:997:2: note: here
  case 3: /* class 3 */
  ^~~~
/kisskb/src/block/genhd.c: In function 'diskstats_show':
/kisskb/src/block/genhd.c:1181:1: warning: the frame size of 1712 bytes is larger than 1280 bytes [-Wframe-larger-than=]
 }
 ^
/kisskb/src/lib/xxhash.c: In function 'xxh64':
/kisskb/src/lib/xxhash.c:236:1: warning: the frame size of 1656 bytes is larger than 1280 bytes [-Wframe-larger-than=]
 }
 ^
Completed OK
# rm -rf /kisskb/build/linus_generic-32bit_defconfig_parisc-gcc8
# Build took: 0:01:42.420576