| Summary: | pthread_cond_destroy does not pass private flag to futex system calls | ||
|---|---|---|---|
| Product: | glibc | Reporter: | Florian Weimer <fweimer> |
| Component: | nptl | Assignee: | Florian Weimer <fweimer> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | drepper.fsp, fweimer |
| Priority: | P2 | Flags: | fweimer:
security-
|
| Version: | unspecified | ||
| Target Milestone: | 2.34 | ||
| See Also: | https://github.com/linux-test-project/ltp/issues/746 | ||
| Host: | Target: | ||
| Build: | Last reconfirmed: | ||
Note that this is sadly unrelated to the libdb/RPM database corruption we see on s390x; we have not backported this into the glibc 2.28 branch where we see this. The master branch has been updated by Florian Weimer <fw@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c4ad832276f4dadfa40904109b26a521468f66bc commit c4ad832276f4dadfa40904109b26a521468f66bc Author: Florian Weimer <fweimer@redhat.com> Date: Thu Feb 4 15:00:20 2021 +0100 nptl: Remove private futex optimization [BZ #27304] It is effectively used, unexcept for pthread_cond_destroy, where we do not want it; see bug 27304. The internal locks do not support a process-shared mode. This fixes commit dc6cfdc934db9997c33728082d63552b9eee4563 ("nptl: Move pthread_cond_destroy implementation into libc"). Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> Fixed for glibc 2.34. It turns out that LTP actually tests for this bug. The release/2.33/master branch has been updated by Florian Weimer <fw@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=79c6be6a0ad59e28cfb73ad6cae6b073e22836e3 commit 79c6be6a0ad59e28cfb73ad6cae6b073e22836e3 Author: Florian Weimer <fweimer@redhat.com> Date: Thu Feb 4 15:00:20 2021 +0100 nptl: Remove private futex optimization [BZ #27304] It is effectively used, unexcept for pthread_cond_destroy, where we do not want it; see bug 27304. The internal locks do not support a process-shared mode. This fixes commit dc6cfdc934db9997c33728082d63552b9eee4563 ("nptl: Move pthread_cond_destroy implementation into libc"). Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> (cherry picked from commit c4ad832276f4dadfa40904109b26a521468f66bc) |
Commit dc6cfdc934db9997c33728082d63552b9eee4563 ("nptl: Move pthread_cond_destroy implementation into libc") dropped use of the process-shared flag because of this optimization in sysdeps/nptl/lowlevellock-futex.h: # if IS_IN (libc) || IS_IN (rtld) /* In libc.so or ld.so all futexes are private. */ # define __lll_private_flag(fl, private) \ ({ \ /* Prevent warnings in callers of this macro. */ \ int __lll_private_flag_priv __attribute__ ((unused)); \ __lll_private_flag_priv = (private); \ ((fl) | FUTEX_PRIVATE_FLAG); \ }) # else # define __lll_private_flag(fl, private) \ (((fl) | FUTEX_PRIVATE_FLAG) ^ (private)) # endif I think the fix is to remove the optimization because it is unused. The internal locks are always private, so the optimization does not matter to them. On x86-64, pthread_cond_destroy is the only place where the alternative macro definition results in changed machine code, but we do not actually want this change there (because it probably breaks process-shared condition variables).