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When running the LTP testsuite one may hit this kernel BUG() with the write06 testcase: kernel BUG at mm/filemap.c:2023! CPU: 1 PID: 8614 Comm: writev01 Not tainted 3.10.0-rc7-64bit-c3000+ #6 IASQ: 0000000000000000 0000000000000000 IAOQ: 00000000401e6e84 00000000401e6e88 IIR: 03ffe01f ISR: 0000000010340000 IOR: 000001fbe0380820 CPU: 1 CR30: 00000000bef80000 CR31: ffffffffffffffff ORIG_R28: 00000000bdc192c0 IAOQ[0]: iov_iter_advance+0x3c/0xc0 IAOQ[1]: iov_iter_advance+0x40/0xc0 RP(r2): generic_file_buffered_write+0x204/0x3f0 Backtrace: [<00000000401e764c>] generic_file_buffered_write+0x204/0x3f0 [<00000000401eab24>] __generic_file_aio_write+0x244/0x448 [<00000000401eadc0>] generic_file_aio_write+0x98/0x150 [<000000004024f460>] do_sync_readv_writev+0xc0/0x130 [<000000004025037c>] compat_do_readv_writev+0x12c/0x340 [<00000000402505f8>] compat_writev+0x68/0xa0 [<0000000040251d88>] compat_SyS_writev+0x98/0xf8 Reason for this crash is a gcc miscompilation in the fault handlers of pa_memcpy() which return the fault address instead of the copied bytes. Since this seems to be a generic problem with gcc-4.7.x (and below), it's better to simplify the fault handlers in pa_memcpy to avoid this problem. Here is a simple reproducer for the problem: int main(int argc, char **argv) { int fd, nbytes; struct iovec wr_iovec[] = { { "TEST STRING ",32}, { (char*)0x40005000,32} }; // random memory. fd = open(DATA_FILE, O_RDWR | O_CREAT, 0666); nbytes = writev(fd, wr_iovec, 2); printf("return value = %d, errno %d (%s)\n", nbytes, errno, strerror(errno)); return 0; } In addition, John David Anglin wrote: There is no gcc PR as pa_memcpy is not legitimate C code. There is an implicit assumption that certain variables will contain correct values when an exception occurs and the code randomly jumps to one of the exception blocks. There is no guarantee of this. If a PR was filed, it would likely be marked as invalid. Signed-off-by: Helge Deller <deller@gmx.de> Signed-off-by: John David Anglin <dave.anglin@bell.net> Cc: <stable@vger.kernel.org> # 3.8+ Signed-off-by: Helge Deller <deller@gmx.de> |
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