From: Amit Shah <amit.shah@redhat.com> To: Sachin Sant <sachinp@in.ibm.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>, Greg Kroah-Hartman <gregkh@suse.de>, a.p.zijlstra@chello.nl, Rusty Russell <rusty@rustcorp.com.au>, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, Anton Blanchard <anton@samba.org>, tglx@linutronix.de, Linus Torvalds <torvalds@linux-foundation.org>, mingo@elte.hu, Alan Cox <alan@lxorguk.ukuu.org.uk> Subject: Re: [PATCH 4/7] hvc_console: Fix race between hvc_close and hvc_remove Date: Fri, 26 Mar 2010 18:13:40 +0530 [thread overview] Message-ID: <20100326124340.GB7039@amit-x200.redhat.com> (raw) In-Reply-To: <4BAC9D9E.5070901@in.ibm.com> On (Fri) Mar 26 2010 [17:12:22], Sachin Sant wrote: > Amit Shah wrote: >> On (Fri) Mar 26 2010 [14:43:56], Sachin Sant wrote: >> >>>> And this suggests that hvc_kick() is called before hvc_task is >>>> initialised, ie, before hvc_init() is called. >>>> >>>> Does this help? >>>> >>> Hi Amit, >>> >>> I too ran into this issue as reported by Anton. Unfortunately in my >>> case the following suggested patch does not help boot the powerpc >>> box successfully. The boot still hangs with following messages >>> >> >> Was the hang you saw before applying this patch at the same place / for >> the same reason? >> > Yes the machine hangs at the same place with or without the patch. OK. >>> mount: can't find /root/proc in /etc/fstab or /etc/mtab >>> /sbin/smart_agetty: can not determine 'console' speed >>> >> >> OK, this gets even murkier. I don't know why taking a few krefs modifies >> hvc_console behaviour to such an extent. >> > Looking at the commit e74d098c66543d0731de62eb747ccd5b636a6f4c, > i see that for every tty_kref_get() there is a corresponding > tty_kref_put() except maybe for the one in the following patch snippet > > spin_lock_irqsave(&hp->lock, flags); > /* Check and then increment for fast path open. */ > if (hp->count++ > 0) { > + tty_kref_get(tty); > spin_unlock_irqrestore(&hp->lock, flags); > hvc_kick(); > return 0; > > I don't know this code very well but we might be missing a > corresponding tty_kref_put() some place ? See hvc_hangup: temp_open_count = hp->count; ... while(temp_open_count) { --temp_open_count; tty_kref_put(tty); kref_put(&hp->kref, destroy_hvc_struct); } > If i comment out the above tty_kref_get() call, the machine > boots fine with or without the suggested patch. Hm, so as Alan suggests, it could be a timing issue in getting the ref and returning back from hvc_open(). I don't know how the tty layer works, but delays in getting the open() succeed results in badness? Guess we'll have to poke at the other drivers to see how they handle open() calls. Amit
WARNING: multiple messages have this Message-ID (diff)
From: Amit Shah <amit.shah@redhat.com> To: Sachin Sant <sachinp@in.ibm.com> Cc: Greg Kroah-Hartman <gregkh@suse.de>, a.p.zijlstra@chello.nl, Rusty Russell <rusty@rustcorp.com.au>, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, Anton Blanchard <anton@samba.org>, tglx@linutronix.de, Linus Torvalds <torvalds@linux-foundation.org>, mingo@elte.hu, Alan Cox <alan@lxorguk.ukuu.org.uk> Subject: Re: [PATCH 4/7] hvc_console: Fix race between hvc_close and hvc_remove Date: Fri, 26 Mar 2010 18:13:40 +0530 [thread overview] Message-ID: <20100326124340.GB7039@amit-x200.redhat.com> (raw) In-Reply-To: <4BAC9D9E.5070901@in.ibm.com> On (Fri) Mar 26 2010 [17:12:22], Sachin Sant wrote: > Amit Shah wrote: >> On (Fri) Mar 26 2010 [14:43:56], Sachin Sant wrote: >> >>>> And this suggests that hvc_kick() is called before hvc_task is >>>> initialised, ie, before hvc_init() is called. >>>> >>>> Does this help? >>>> >>> Hi Amit, >>> >>> I too ran into this issue as reported by Anton. Unfortunately in my >>> case the following suggested patch does not help boot the powerpc >>> box successfully. The boot still hangs with following messages >>> >> >> Was the hang you saw before applying this patch at the same place / for >> the same reason? >> > Yes the machine hangs at the same place with or without the patch. OK. >>> mount: can't find /root/proc in /etc/fstab or /etc/mtab >>> /sbin/smart_agetty: can not determine 'console' speed >>> >> >> OK, this gets even murkier. I don't know why taking a few krefs modifies >> hvc_console behaviour to such an extent. >> > Looking at the commit e74d098c66543d0731de62eb747ccd5b636a6f4c, > i see that for every tty_kref_get() there is a corresponding > tty_kref_put() except maybe for the one in the following patch snippet > > spin_lock_irqsave(&hp->lock, flags); > /* Check and then increment for fast path open. */ > if (hp->count++ > 0) { > + tty_kref_get(tty); > spin_unlock_irqrestore(&hp->lock, flags); > hvc_kick(); > return 0; > > I don't know this code very well but we might be missing a > corresponding tty_kref_put() some place ? See hvc_hangup: temp_open_count = hp->count; ... while(temp_open_count) { --temp_open_count; tty_kref_put(tty); kref_put(&hp->kref, destroy_hvc_struct); } > If i comment out the above tty_kref_get() call, the machine > boots fine with or without the suggested patch. Hm, so as Alan suggests, it could be a timing issue in getting the ref and returning back from hvc_open(). I don't know how the tty layer works, but delays in getting the open() succeed results in badness? Guess we'll have to poke at the other drivers to see how they handle open() calls. Amit
next prev parent reply other threads:[~2010-03-26 12:46 UTC|newest] Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-03-19 15:13 [GIT PATCH] TTY fixes for 2.6.34-git Greg KH 2010-03-19 15:18 ` [PATCH 1/7] Revert "tty: Add a new VT mode which is like VT_PROCESS but doesn't require a VT_RELDISP ioctl call" Greg Kroah-Hartman 2010-03-19 15:18 ` [PATCH 2/7] tty: Take a 256 byte padding into account when buffering below sub-page units Greg Kroah-Hartman 2010-03-19 15:18 ` [PATCH 3/7] uartlite: Fix build on sparc Greg Kroah-Hartman 2010-03-19 16:15 ` Grant Likely 2010-03-19 16:26 ` Grant Likely 2010-03-26 14:31 ` Michal Simek 2010-03-19 15:18 ` [PATCH 4/7] hvc_console: Fix race between hvc_close and hvc_remove Greg Kroah-Hartman 2010-03-19 15:18 ` Greg Kroah-Hartman 2010-03-20 21:04 ` Benjamin Herrenschmidt 2010-03-20 21:04 ` Benjamin Herrenschmidt 2010-03-21 4:37 ` Amit Shah 2010-03-21 4:37 ` Amit Shah 2010-03-24 12:19 ` Amit Shah 2010-03-24 12:19 ` Amit Shah 2010-03-25 23:30 ` Anton Blanchard 2010-03-25 23:30 ` Anton Blanchard 2010-03-26 2:01 ` Amit Shah 2010-03-26 2:01 ` Amit Shah 2010-03-26 9:13 ` Sachin Sant 2010-03-26 9:13 ` Sachin Sant 2010-03-26 9:58 ` Amit Shah 2010-03-26 9:58 ` Amit Shah 2010-03-26 10:54 ` Stephen Rothwell 2010-03-26 10:54 ` Stephen Rothwell 2010-03-26 11:42 ` Sachin Sant 2010-03-26 11:42 ` Sachin Sant 2010-03-26 11:52 ` Alan Cox 2010-03-26 11:52 ` Alan Cox 2010-03-26 12:49 ` Amit Shah 2010-03-26 12:49 ` Amit Shah 2010-03-26 12:43 ` Amit Shah [this message] 2010-03-26 12:43 ` Amit Shah 2010-04-06 11:42 ` Anton Blanchard 2010-04-06 11:42 ` Anton Blanchard 2010-04-06 12:09 ` Amit Shah 2010-04-06 12:09 ` Amit Shah 2010-04-06 12:27 ` Sachin Sant 2010-04-06 12:27 ` Sachin Sant 2010-04-06 12:32 ` Alan Cox 2010-04-06 12:32 ` Alan Cox 2010-04-08 0:26 ` Rusty Russell 2010-04-08 0:26 ` Rusty Russell 2010-03-24 10:45 ` Benjamin Herrenschmidt 2010-03-24 10:45 ` Benjamin Herrenschmidt 2010-03-24 10:57 ` Amit Shah 2010-03-24 10:57 ` Amit Shah 2010-03-24 11:37 ` Alan Cox 2010-03-24 11:37 ` Alan Cox 2010-03-24 15:05 ` Amit Shah 2010-03-24 15:05 ` Amit Shah 2010-03-19 15:18 ` [PATCH 5/7] tty_buffer: Fix distinct type warning Greg Kroah-Hartman 2010-03-19 15:18 ` [PATCH 6/7] tty: cpm_uart: use resource_size() Greg Kroah-Hartman 2010-03-19 15:18 ` [PATCH 7/7] tty_port,usb-console: Fix usb serial console open/close regression Greg Kroah-Hartman
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20100326124340.GB7039@amit-x200.redhat.com \ --to=amit.shah@redhat.com \ --cc=a.p.zijlstra@chello.nl \ --cc=alan@lxorguk.ukuu.org.uk \ --cc=anton@samba.org \ --cc=benh@kernel.crashing.org \ --cc=gregkh@suse.de \ --cc=linux-kernel@vger.kernel.org \ --cc=linuxppc-dev@ozlabs.org \ --cc=mingo@elte.hu \ --cc=rusty@rustcorp.com.au \ --cc=sachinp@in.ibm.com \ --cc=tglx@linutronix.de \ --cc=torvalds@linux-foundation.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.