Messages in this thread | | | Date | Tue, 15 Nov 2011 01:14:06 +0200 | From | Denis Kuzmenko <> | Subject | Re: [PATCH] gpio/gpio-sysfs: Try to export busy GPIO line leads to wrong GPIO line exporting |
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On 11/14/2011 10:45 PM, Stephen Warren wrote: > Denis Kuzmenko wrote at Saturday, November 12, 2011 6:31 PM: >> >> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c >> index a971e3d..ccec497 100644 >> --- a/drivers/gpio/gpiolib.c >> +++ b/drivers/gpio/gpiolib.c >> @@ -633,7 +633,7 @@ static ssize_t export_store(struct class *class, >> done: >> if (status) >> pr_debug("%s: status %d\n", __func__, status); >> - return status ? : len; >> + return len; >> } > > I assume that when the error occurs, status is negative. Is it some > special value like EINTR, EAGAIN? I'm surprised that the retried write > is smaller than the whole original buffer. > > What's actually retrying the failed write? Is it user-space in response > to the previous failed write, in a (mistaken?) attempt to handle shorter- > than-expected-writes? You could confirm this with strace. > > If the patch above really is correct, there are other places it'd be > needed; it looks like e.g. drivers/video/backlight/backlight.c would > have the same issue if you gave too-large integers to its sysfs files. >
Hi,
Looks like userspace doesn't retries write. Here is trace:
open("/sys/class/gpio/export", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3 ioctl(3, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbef76c64) = -1 ENOTTY (Inappropriate ioctl for device) brk(0x30e000) = 0x30e000 write(3, "37\n", 3) = -1 EBUSY (Device or resource busy) close(3) = 0 exit(0) = ?
this was made by simple self-written program: fopen("/sys/class/gpio/export", "w"); fprintf(fp, "37\n");
additional kernel-trace (WARN_ON(0 > status)) was also added before function return:
WARNING: at drivers/gpio/gpiolib.c:637 export_store+0xa0/0xb4() Modules linked in: [<c0028064>] (unwind_backtrace+0x0/0xf0) from [<c0039234>] (warn_slowpath_common+0x48/0x60) [<c0039234>] (warn_slowpath_common+0x48/0x60) from [<c0039268>] (warn_slowpath_null+0x1c/0x24) [<c0039268>] (warn_slowpath_null+0x1c/0x24) from [<c0182da8>] (export_store+0xa0/0xb4) [<c0182da8>] (export_store+0xa0/0xb4) from [<c01b17e0>] (class_attr_store+0x1c/0x28) [<c01b17e0>] (class_attr_store+0x1c/0x28) from [<c00db9ac>] (sysfs_write_file+0xfc/0x180) [<c00db9ac>] (sysfs_write_file+0xfc/0x180) from [<c0093304>] (vfs_write+0xac/0x13c) [<c0093304>] (vfs_write+0xac/0x13c) from [<c0093578>] (sys_write+0x40/0x6c) [<c0093578>] (sys_write+0x40/0x6c) from [<c0023ffc>] (__sys_trace_return+0x0/0x24) ---[ end trace 8141a98436c712ec ]---
I'll try digg into functions in backtrace and find retry if any.
Best regards, Denis Kuzmenko.
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