Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754121Ab2K2Rsy (ORCPT ); Thu, 29 Nov 2012 12:48:54 -0500 Received: from 95-31-19-74.broadband.corbina.ru ([95.31.19.74]:51670 "EHLO 95-31-19-74.broadband.corbina.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753956Ab2K2Rsw (ORCPT ); Thu, 29 Nov 2012 12:48:52 -0500 Message-ID: <50B79FF4.4020201@ilyx.ru> Date: Thu, 29 Nov 2012 21:48:36 +0400 From: Ilya Zykov User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:16.0) Gecko/20121026 Thunderbird/16.0.2 MIME-Version: 1.0 To: Alan Cox CC: Xiaobing Tu , Alan Cox , Jiri Slaby , Alek Du , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Subject: Re: [PATCH] tty: Correct tty buffer flushing. References: <50B55A93.4090900@ilyx.ru> <50B6A652.9000107@ilyx.ru> <20121129135418.4237e7f8@pyramind.ukuu.org.uk> In-Reply-To: <20121129135418.4237e7f8@pyramind.ukuu.org.uk> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6855 Lines: 136 On 29.11.2012 17:54, Alan Cox wrote: >> diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c >> index 6c9b7cd..4f02f9c 100644 >> --- a/drivers/tty/tty_buffer.c >> +++ b/drivers/tty/tty_buffer.c >> @@ -114,11 +114,14 @@ static void __tty_buffer_flush(struct tty_struct *tty) >> { >> struct tty_buffer *thead; >> >> - while ((thead = tty->buf.head) != NULL) { >> - tty->buf.head = thead->next; >> - tty_buffer_free(tty, thead); >> + if (tty->buf.head == NULL) >> + return; >> + while ((thead = tty->buf.head->next) != NULL) { >> + tty_buffer_free(tty, tty->buf.head); >> + tty->buf.head = thead; > > This part of the change seems to have no effect at all. There are no > locks held so there is nothing guaranteeing how the other processors > views of the order of operations will be affected. > > Alan > Test program for this problem, after revert "commit f8f72f047" without "[PATCH] tty: Correct tty buffer flushing.", it cause of "BUG report"(see below) on SMP system linux-3.7.0-rc7. Both patches resolve problem for this test. But my patch is more right.IMHO. And also fix problem with tty_prepare_string*(). Thank you. ---------------------------------------------------------------------- #include #include #include #include #include #define BUF_SIZE 4 #define ERROR_EXIT_CODE 1 #define parent child_id static int mfd=-1, sfd=-1, parent=1; static char pty_name[24]; static void pty_exit(int ret, char * exit_message){ if (sfd >= 0) close(sfd); if (mfd >= 0) close(mfd); printf("%s %s exit. \n %s",ret?"Error":"Normal", parent?"parent":"child", exit_message?exit_message:""); exit(ret); } static void pty_init(void){ int ptn; if( (mfd=open("/dev/ptmx", O_RDWR )) < 0 ) pty_exit(ERROR_EXIT_CODE,"Couldn't open /dev/ptmx. \n"); if (ioctl(mfd, TIOCGPTN, &ptn) < 0 ) pty_exit(ERROR_EXIT_CODE,"Couldn't get pty number. \n"); snprintf(pty_name, sizeof(pty_name), "/dev/pts/%d", ptn); printf("Slave pty name = %s.\n",pty_name); ptn=0; if (ioctl(mfd, TIOCSPTLCK, &ptn) < 0 ) pty_exit(ERROR_EXIT_CODE,"Couldn't unlock pty slave. \n"); if ( (sfd=open(pty_name, O_RDWR )) < 0 ) pty_exit(ERROR_EXIT_CODE, "Couldn't open pty slave. \n"); } int main(int argc,char *argv[]) { pty_init(); char buf[]={ [0 ... BUF_SIZE-1]='1' }; child_id=fork(); do { if(parent) { if ( write(mfd, buf, BUF_SIZE) < 0 ) pty_exit(ERROR_EXIT_CODE, "Parent's write() error.\n"); } else { //Child if ( tcflush(sfd, TCIFLUSH) < 0 ) pty_exit(ERROR_EXIT_CODE, "Child's tcflush() error.\n"); } } while(1); return 0; //Never } ---------------------------------------------------------------------- Nov 29 20:42:07 bm kernel: BUG: unable to handle kernel NULL pointer dereference at 0000000000000018 Nov 29 20:42:07 bm kernel: IP: [] tty_insert_flip_string_fixed_flag+0x74/0xd0 Nov 29 20:42:07 bm kernel: PGD 114bc8067 PUD 11149d067 PMD 0 Nov 29 20:42:07 bm kernel: Oops: 0000 [#1] SMP Nov 29 20:42:07 bm kernel: Modules linked in: fuse autofs4 sunrpc cpufreq_ondemand acpi_cpufreq freq_table mperf ipt_REJECT nf_conntrack_ipv4 nf_defrag_ipv4 iptable_filter ip_tables ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables ipv6 dm_mirror dm_region_hash dm_log dm_mod uinput iTCO_wdt iTCO_vendor_support gpio_ich sg joydev coretemp kvm_intel kvm microcode pcspkr serio_raw i2c_i801 asus_atk0110 hwmon lpc_ich sky2 snd_hda_codec_analog snd_hda_intel snd_hda_codec snd_hwdep snd_seq snd_seq_device snd_pcm snd_timer snd soundcore snd_page_alloc nvidia(PO) ext3 jbd mbcache sr_mod cdrom sd_mod crc_t10dif pata_acpi ata_generic pata_jmicron ahci libahci Nov 29 20:42:07 bm kernel: CPU 1 Nov 29 20:42:07 bm kernel: Pid: 8953, comm: a.out Tainted: P O 3.7.0-rc7-1+ #23 System manufacturer P5K Premium/P5K Premium Nov 29 20:42:07 bm kernel: RIP: 0010:[] [] tty_insert_flip_string_fixed_flag+0x74/0xd0 Nov 29 20:42:07 bm kernel: RSP: 0018:ffff88011dee5d58 EFLAGS: 00010202 Nov 29 20:42:07 bm kernel: RAX: 0000000000000004 RBX: ffff88012934d000 RCX: ffff880119cfbc00 Nov 29 20:42:07 bm kernel: RDX: 0000000000000246 RSI: ffff880112de1800 RDI: 0000000000000246 Nov 29 20:42:07 bm kernel: RBP: ffff88011dee5da8 R08: ffff880112de1800 R09: 0000000000000000 Nov 29 20:42:07 bm kernel: R10: 00007fffcd7827a0 R11: 0000000000000246 R12: 0000000000000000 Nov 29 20:42:07 bm kernel: R13: 0000000000000004 R14: 0000000000000004 R15: 0000000000000004 Nov 29 20:42:07 bm kernel: FS: 00007f1e28985700(0000) GS:ffff88012fc80000(0000) knlGS:0000000000000000 Nov 29 20:42:07 bm kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b Nov 29 20:42:07 bm kernel: CR2: 0000000000000018 CR3: 0000000110321000 CR4: 00000000000407e0 Nov 29 20:42:07 bm kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 Nov 29 20:42:07 bm kernel: DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Nov 29 20:42:07 bm kernel: Process a.out (pid: 8953, threadinfo ffff88011dee4000, task ffff880128ba80c0) Nov 29 20:42:07 bm kernel: Stack: Nov 29 20:42:07 bm kernel: ffff88011dee5e78 0000000028852800 ffff880112de1800 0000000000000004 Nov 29 20:42:07 bm kernel: 0000000000000004 ffff880128852800 ffff88012934d000 ffff880112de1800 Nov 29 20:42:07 bm kernel: 0000000000000004 ffff880112de1800 ffff88011dee5dd8 ffffffff8134444b Nov 29 20:42:07 bm kernel: Call Trace: Nov 29 20:42:07 bm kernel: [] pty_write+0x3b/0x80 Nov 29 20:42:07 bm kernel: [] ? add_wait_queue+0x4e/0x60 Nov 29 20:42:07 bm kernel: [] n_tty_write+0x210/0x2e0 Nov 29 20:42:07 bm kernel: [] ? try_to_wake_up+0x2b0/0x2b0 Nov 29 20:42:07 bm kernel: [] tty_write+0x1b1/0x290 Nov 29 20:42:07 bm kernel: [] ? n_tty_ioctl+0xf0/0xf0 Nov 29 20:42:07 bm kernel: [] vfs_write+0xc8/0x190 Nov 29 20:42:07 bm kernel: [] sys_write+0x5f/0xa0 Nov 29 20:42:07 bm kernel: [] ? __audit_syscall_exit+0x426/0x480 Nov 29 20:42:07 bm kernel: [] system_call_fastpath+0x16/0x1b Nov 29 20:42:07 bm kernel: Code: 00 07 00 00 48 0f 47 f0 48 63 f6 e8 47 fd ff ff 85 c0 41 89 c5 4c 8b a3 a8 01 00 00 74 42 48 98 48 8b 75 c0 45 01 ee 48 89 45 c8 <49> 63 7c 24 18 48 89 c2 49 03 7c 24 08 e8 9a 32 f4 ff 49 63 7c Nov 29 20:42:07 bm kernel: RIP [] tty_insert_flip_string_fixed_flag+0x74/0xd0 Nov 29 20:42:07 bm kernel: RSP Nov 29 20:42:07 bm kernel: CR2: 0000000000000018 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/