linux-kernel - Re: [PATCH 1/1] Char: isicom, fix card locking

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Message-ID: <45776D4F.6070806@gmail.com>
Date:	Thu, 07 Dec 2006 02:24:08 +0059
From:	Jiri Slaby <jirislaby@...il.com>
To:	Eric Fox <efox@...steinindustries.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] Char: isicom, fix card locking

Eric Fox wrote:
> Patch works if I disable SMP in kernel.

Aha, and it didn't work without the patch with SMP disabled?

> strace setserial -g /dev/ttyM0
> execve("/bin/setserial", ["setserial", "-g", "/dev/ttyM0"], [/* 17 vars
> */]) = 0
> uname({sys="Linux", node="dialin-0.vab.com", ...}) = 0
> brk(0)                                  = 0x804d000
> access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or
> directory)
> open("/etc/ld.so.cache", O_RDONLY)      = 3
> fstat64(3, {st_mode=S_IFREG|0644, st_size=19713, ...}) = 0
> old_mmap(NULL, 19713, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7f58000
> close(3)                                = 0
> open("/lib/tls/libc.so.6", O_RDONLY)    = 3
> read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\320\36"..., 512) =
> 512
> fstat64(3, {st_mode=S_IFREG|0755, st_size=1454802, ...}) = 0
> old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
> 0) = 0xb7f57000
> old_mmap(0x39d000, 1223900, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE,
> 3, 0) = 0x39d000
> old_mmap(0x4c2000, 16384, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x124000) = 0x4c2000
> old_mmap(0x4c6000, 7388, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x4c6000
> close(3)                                = 0
> old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
> 0) = 0xb7f56000
> mprotect(0x4c2000, 4096, PROT_READ)     = 0
> mprotect(0x399000, 4096, PROT_READ)     = 0
> set_thread_area({entry_number:-1 -> 6, base_addr:0xb7f566c0, limit:1048575,
> seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1,
> seg_not_present:0, 0munmap(0xb7f58000, 19713)               = 0


> open("/dev/ttyM0", O_RDWR|O_NONBLOCK)   = 3
> ioctl(3, TIOCGSERIAL, 0xbf81c280)       = 0

In one of these two there should lie the problem in SMP mode. The latter is OK
(no locking), but the former -- hmm, it gets stuck: I guess, we have a recursive
locking example here (I can see one of many in the driver now):
isicom_open()
{
...
isicom_setup_port()
...
}

isicom_setup_port()
{
...
        spin_lock_irqsave(&card->card_lock, flags);
...
        isicom_config_port();
...
        spin_unlock_irqrestore(&card->card_lock, flags);
}

isicom_config_port()
{
...
	lock_card()
...
	unlock_card()
...
}

lock_card()
{
...
	spin_lock_irqsave(&card->card_lock, card->flags);
...
}

unlock_card()
{
	spin_unlock_irqrestore(&card->card_lock, card->flags);
}

Going to fix these.

thanks,
-- 
http://www.fi.muni.cz/~xslaby/            Jiri Slaby
faculty of informatics, masaryk university, brno, cz
e-mail: jirislaby gmail com, gpg pubkey fingerprint:
B674 9967 0407 CE62 ACC8  22A0 32CC 55C3 39D4 7A7E
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