From: Anton Vorontsov Date: Thu, 31 May 2012 23:26:24 +0000 (-0700) Subject: blackfin: fix possible deadlock in decode_address() X-Git-Tag: Ubuntu-5.10.0-12.13~21328^2~32 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=af1be5a578a1ccc9961c55290f8c509a00a69036;p=mirror_ubuntu-hirsute-kernel.git blackfin: fix possible deadlock in decode_address() Oleg Nesterov found an interesting deadlock possibility: > sysrq_showregs_othercpus() does smp_call_function(showacpu) > and showacpu() show_stack()->decode_address(). Now suppose that IPI > interrupts the task holding read_lock(tasklist). To fix this, blackfin should not grab the write_ variant of the tasklist lock, read_ one is enough. Suggested-by: Oleg Nesterov Signed-off-by: Anton Vorontsov Cc: Mike Frysinger Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/arch/blackfin/kernel/trace.c b/arch/blackfin/kernel/trace.c index d08f0e3e2dcc..f7f7a18abca9 100644 --- a/arch/blackfin/kernel/trace.c +++ b/arch/blackfin/kernel/trace.c @@ -29,7 +29,7 @@ void decode_address(char *buf, unsigned long address) { struct task_struct *p; struct mm_struct *mm; - unsigned long flags, offset; + unsigned long offset; struct rb_node *n; #ifdef CONFIG_KALLSYMS @@ -113,7 +113,7 @@ void decode_address(char *buf, unsigned long address) * mappings of all our processes and see if we can't be a whee * bit more specific */ - write_lock_irqsave(&tasklist_lock, flags); + read_lock(&tasklist_lock); for_each_process(p) { struct task_struct *t; @@ -186,7 +186,7 @@ __continue: sprintf(buf, "/* kernel dynamic memory */"); done: - write_unlock_irqrestore(&tasklist_lock, flags); + read_unlock(&tasklist_lock); } #define EXPAND_LEN ((1 << CONFIG_DEBUG_BFIN_HWTRACE_EXPAND_LEN) * 256 - 1)