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  1. MariaDB Server
  2. MDEV-26601

Incorrect use of O_TMPFILE

Details

    Description

      I noticed this line in mysql.err:

      2021-09-13 16:11:44 0 [Note] mysqld: O_TMPFILE is not supported on /tmp (disabling future attempts)

      However, /tmp is a tmpfs which does support O_TMPFILE. The issue is that mysqld calls open incorrectly:

      [pid 11696] openat(AT_FDCWD, "/tmp", O_RDWR|O_CREAT|O_TRUNC|O_CLOEXEC|O_TMPFILE, 0660) = -1 EINVAL
      		 
      [pid 11696] openat(AT_FDCWD, "/tmp/ibMbcqxC", O_RDWR|O_CREAT|O_EXCL|O_CLOEXEC, 0600) = 8
      		 
      [pid 11696] unlink("/tmp/ibMbcqxC")     = 0

      Either O_CREAT or O_TMPFILE can be specified, but not both at the same time. This effectively makes the O_TMPFILE support dead code.

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          is caused by

          Bug - A problem which impairs or prevents the functions of the product. MDEV-15584 Linux - use O_TMPFILE for create_temp_file

          • Major - Major loss of function.
          • Closed

          Activity

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            danblack Daniel Black added a comment -

            Thanks Fabian. I never noticed because of the description in https://man7.org/linux/man-pages/man2/open.2.html

            Local test:

            diff --git a/mysys/mf_tempfile.c b/mysys/mf_tempfile.c
            		 
            index 51a3efa05ad..0f1c6d6b1bc 100644
            		 
            --- a/mysys/mf_tempfile.c
            		 
            +++ b/mysys/mf_tempfile.c
            		 
            @@ -121,7 +121,7 @@ File create_temp_file(char *to, const char *dir, const char *prefix,
            		 
                   /* explictly don't use O_EXCL here has it has a different
            		 
                      meaning with O_TMPFILE
            		 
                   */
            		 
            -      if ((file= open(dir, mode | O_TMPFILE | O_CLOEXEC,
            		 
            +      if ((file= open(dir, (mode & ~O_CREAT) | O_TMPFILE | O_CLOEXEC,
            		 
                                   S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP)) >= 0)
            		 
                   {
            		 
                     my_snprintf(to, FN_REFLEN, "%s/#sql/fd=%d", dir, file);


            strace: Process 2240978 attached
            		 
            2021-09-14 19:01:15 0 [Note] InnoDB: Using Linux native AIO
            		 
            2021-09-14 19:01:15 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
            		 
            2021-09-14 19:01:15 0 [Note] InnoDB: Uses event mutexes
            		 
            2021-09-14 19:01:15 0 [Note] InnoDB: Compressed tables use zlib 1.2.11
            		 
            2021-09-14 19:01:15 0 [Note] InnoDB: Number of pools: 1
            		 
            2021-09-14 19:01:15 0 [Note] InnoDB: Using SSE2 crc32 instructions
            		 
            [pid 2240976] openat(AT_FDCWD, "/tmp", O_RDWR|O_TRUNC|O_CLOEXEC|O_TMPFILE, 0660) = 6
            		 
            [pid 2240976] openat(AT_FDCWD, "/tmp", O_RDWR|O_TRUNC|O_CLOEXEC|O_TMPFILE, 0660) = 6
            		 
            [pid 2240976] openat(AT_FDCWD, "/tmp", O_RDWR|O_TRUNC|O_CLOEXEC|O_TMPFILE, 0660) = 6

            where /tmp/ is a tmpfs.

            danblack Daniel Black added a comment - Thanks Fabian. I never noticed because of the description in https://man7.org/linux/man-pages/man2/open.2.html Local test: diff --git a/mysys/mf_tempfile.c b/mysys/mf_tempfile.c index 51a3efa05ad..0f1c6d6b1bc 100644 --- a/mysys/mf_tempfile.c +++ b/mysys/mf_tempfile.c @@ -121,7 +121,7 @@ File create_temp_file(char *to, const char *dir, const char *prefix, /* explictly don't use O_EXCL here has it has a different meaning with O_TMPFILE */ - if ((file= open(dir, mode | O_TMPFILE | O_CLOEXEC, + if ((file= open(dir, (mode & ~O_CREAT) | O_TMPFILE | O_CLOEXEC, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP)) >= 0) { my_snprintf(to, FN_REFLEN, "%s/#sql/fd=%d", dir, file); strace: Process 2240978 attached 2021-09-14 19:01:15 0 [Note] InnoDB: Using Linux native AIO 2021-09-14 19:01:15 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins 2021-09-14 19:01:15 0 [Note] InnoDB: Uses event mutexes 2021-09-14 19:01:15 0 [Note] InnoDB: Compressed tables use zlib 1.2.11 2021-09-14 19:01:15 0 [Note] InnoDB: Number of pools: 1 2021-09-14 19:01:15 0 [Note] InnoDB: Using SSE2 crc32 instructions [pid 2240976] openat(AT_FDCWD, "/tmp", O_RDWR|O_TRUNC|O_CLOEXEC|O_TMPFILE, 0660) = 6 [pid 2240976] openat(AT_FDCWD, "/tmp", O_RDWR|O_TRUNC|O_CLOEXEC|O_TMPFILE, 0660) = 6 [pid 2240976] openat(AT_FDCWD, "/tmp", O_RDWR|O_TRUNC|O_CLOEXEC|O_TMPFILE, 0660) = 6 where /tmp/ is a tmpfs.
            fvogt Fabian Vogt added a comment -

            Great!

            Thanks Fabian. I never noticed because of the description in https://man7.org/linux/man-pages/man2/open.2.html

            Yes, it's really not clear on that topic. I actually did the same error while writing a test program for this, which in some way made it easier for me to spot the bug with strace

            fvogt Fabian Vogt added a comment - Great! Thanks Fabian. I never noticed because of the description in https://man7.org/linux/man-pages/man2/open.2.html Yes, it's really not clear on that topic. I actually did the same error while writing a test program for this, which in some way made it easier for me to spot the bug with strace

            People

              danblack Daniel Black
              fvogt Fabian Vogt
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                Updated:
                Resolved:

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