• Eiichi Tsukata's avatar
    tracing/snapshot: Resize spare buffer if size changed · 90b89546
    Eiichi Tsukata authored
    commit 46cc0b44428d0f0e81f11ea98217fc0edfbeab07 upstream.
    
    Current snapshot implementation swaps two ring_buffers even though their
    sizes are different from each other, that can cause an inconsistency
    between the contents of buffer_size_kb file and the current buffer size.
    
    For example:
    
      # cat buffer_size_kb
      7 (expanded: 1408)
      # echo 1 > events/enable
      # grep bytes per_cpu/cpu0/stats
      bytes: 1441020
      # echo 1 > snapshot             // current:1408, spare:1408
      # echo 123 > buffer_size_kb     // current:123,  spare:1408
      # echo 1 > snapshot             // current:1408, spare:123
      # grep bytes per_cpu/cpu0/stats
      bytes: 1443700
      # cat buffer_size_kb
      123                             // != current:1408
    
    And also, a similar per-cpu case hits the following WARNING:
    
    Reproducer:
    
      # echo 1 > per_cpu/cpu0/snapshot
      # echo 123 > buffer_size_kb
      # echo 1 > per_cpu/cpu0/snapshot
    
    WARNING:
    
      WARNING: CPU: 0 PID: 1946 at kernel/trace/trace.c:1607 update_max_tr_single.part.0+0x2b8/0x380
      Modules linked in:
      CPU: 0 PID: 1946 Comm: bash Not tainted 5.2.0-rc6 #20
      Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-2.fc30 04/01/2014
      RIP: 0010:update_max_tr_single.part.0+0x2b8/0x380
      Code: ff e8 dc da f9 ff 0f 0b e9 88 fe ff ff e8 d0 da f9 ff 44 89 ee bf f5 ff ff ff e8 33 dc f9 ff 41 83 fd f5 74 96 e8 b8 da f9 ff <0f> 0b eb 8d e8 af da f9 ff 0f 0b e9 bf fd ff ff e8 a3 da f9 ff 48
      RSP: 0018:ffff888063e4fca0 EFLAGS: 00010093
      RAX: ffff888066214380 RBX: ffffffff99850fe0 RCX: ffffffff964298a8
      RDX: 0000000000000000 RSI: 00000000fffffff5 RDI: 0000000000000005
      RBP: 1ffff1100c7c9f96 R08: ffff888066214380 R09: ffffed100c7c9f9b
      R10: ffffed100c7c9f9a R11: 0000000000000003 R12: 0000000000000000
      R13: 00000000ffffffea R14: ffff888066214380 R15: ffffffff99851060
      FS:  00007f9f8173c700(0000) GS:ffff88806d000000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 0000000000714dc0 CR3: 0000000066fa6000 CR4: 00000000000006f0
      Call Trace:
       ? trace_array_printk_buf+0x140/0x140
       ? __mutex_lock_slowpath+0x10/0x10
       tracing_snapshot_write+0x4c8/0x7f0
       ? trace_printk_init_buffers+0x60/0x60
       ? selinux_file_permission+0x3b/0x540
       ? tracer_preempt_off+0x38/0x506
       ? trace_printk_init_buffers+0x60/0x60
       __vfs_write+0x81/0x100
       vfs_write+0x1e1/0x560
       ksys_write+0x126/0x250
       ? __ia32_sys_read+0xb0/0xb0
       ? do_syscall_64+0x1f/0x390
       do_syscall_64+0xc1/0x390
       entry_SYSCALL_64_after_hwframe+0x49/0xbe
    
    This patch adds resize_buffer_duplicate_size() to check if there is a
    difference between current/spare buffer sizes and resize a spare buffer
    if necessary.
    
    Link: http://lkml.kernel.org/r/20190625012910.13109-1-devel@etsukata.com
    
    Cc: stable@vger.kernel.org
    Fixes: ad909e21 ("tracing: Add internal tracing_snapshot() functions")
    Signed-off-by: default avatarEiichi Tsukata <devel@etsukata.com>
    Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    90b89546
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