Messages in this thread Patch in this message | | | Date | Tue, 26 Feb 2008 13:32:22 +0100 | From | Jean Delvare <> | Subject | Re: [PATCH] video: limit stack usage of ir-kbd-i2c.c |
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Hi Marcin,
On Mon, 25 Feb 2008 21:51:00 +0100, Marcin Slusarz wrote: > ir_probe allocated struct i2c_client on stack; > it's pretty big structure, so allocate it with kzalloc > > make checkstack output without this patch: > x059d ir_probe [ir-kbd-i2c]: 1000 > > compile tested only > > Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com> > Cc: Mauro Carvalho Chehab <mchehab@infradead.org> > Cc: Jean Delvare <khali@linux-fr.org> > --- > drivers/media/video/ir-kbd-i2c.c | 18 +++++++++++------- > 1 files changed, 11 insertions(+), 7 deletions(-) > > diff --git a/drivers/media/video/ir-kbd-i2c.c b/drivers/media/video/ir-kbd-i2c.c > index 9851987..aec122f 100644 > --- a/drivers/media/video/ir-kbd-i2c.c > +++ b/drivers/media/video/ir-kbd-i2c.c > @@ -510,9 +510,9 @@ static int ir_probe(struct i2c_adapter *adap) > static const int probe_cx88[] = { 0x18, 0x6b, 0x71, -1 }; > static const int probe_cx23885[] = { 0x6b, -1 }; > const int *probe = NULL; > - struct i2c_client c; > + struct i2c_client *c; > unsigned char buf; > - int i,rc; > + int i, rc; > > switch (adap->id) { > case I2C_HW_B_BT848: > @@ -537,19 +537,23 @@ static int ir_probe(struct i2c_adapter *adap) > if (NULL == probe) > return 0; > > - memset(&c,0,sizeof(c)); > - c.adapter = adap; > + c = kzalloc(sizeof(*c), GFP_KERNEL); > + if (!c) > + return -ENOMEM; > + > + c->adapter = adap; > for (i = 0; -1 != probe[i]; i++) { > - c.addr = probe[i]; > - rc = i2c_master_recv(&c,&buf,0); > + c->addr = probe[i]; > + rc = i2c_master_recv(c, &buf, 0); > dprintk(1,"probe 0x%02x @ %s: %s\n", > probe[i], adap->name, > (0 == rc) ? "yes" : "no"); > if (0 == rc) { > - ir_attach(adap,probe[i],0,0); > + ir_attach(adap, probe[i], 0, 0); > break; > } > } > + kfree(c); > return 0; > } >
While this works, I'd rather change the code to call i2c_transfer() instead of i2c_master_recv(). i2c_transfer() is meant exactly for this case (no i2c_client at hand.) This solves the stack usage problem without requiring a temporary memory allocation:
* * * * *
Limit stack usage in ir_probe by calling i2c_transfer, which doesn't require a struct i2c_client, instead of i2c_master_recv which does.
Signed-off-by: Jean Delvare <khali@linux-fr.org> --- drivers/media/video/ir-kbd-i2c.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-)
--- linux-2.6.25-rc3.orig/drivers/media/video/ir-kbd-i2c.c 2008-02-26 11:35:51.000000000 +0100 +++ linux-2.6.25-rc3/drivers/media/video/ir-kbd-i2c.c 2008-02-26 11:44:54.000000000 +0100 @@ -510,8 +510,11 @@ static int ir_probe(struct i2c_adapter * static const int probe_cx88[] = { 0x18, 0x6b, 0x71, -1 }; static const int probe_cx23885[] = { 0x6b, -1 }; const int *probe = NULL; - struct i2c_client c; - unsigned char buf; + struct i2c_msg msg = { + .flags = I2C_M_RD, + .len = 0, + .buf = NULL, + }; int i,rc; switch (adap->id) { @@ -537,15 +540,13 @@ static int ir_probe(struct i2c_adapter * if (NULL == probe) return 0; - memset(&c,0,sizeof(c)); - c.adapter = adap; for (i = 0; -1 != probe[i]; i++) { - c.addr = probe[i]; - rc = i2c_master_recv(&c,&buf,0); + msg.addr = probe[i]; + rc = i2c_transfer(adap, &msg, 1); dprintk(1,"probe 0x%02x @ %s: %s\n", probe[i], adap->name, - (0 == rc) ? "yes" : "no"); - if (0 == rc) { + (1 == rc) ? "yes" : "no"); + if (1 == rc) { ir_attach(adap,probe[i],0,0); break; }
Built-tested, I've also tested loading the ir-kbd-i2c driver on an unsupported cx88 adapter. Review and more testing welcome.
-- Jean Delvare
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