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efivars: retry open and read operations

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On my laptop (Lenovo X1carbo 4th) I very occasionally see test-boot-timestamps
fail with this tb:

262/494 test-boot-timestamps                    FAIL    0.7348453998565674 s (killed by signal 6 SIGABRT)

08:12:48 SYSTEMD_LANGUAGE_FALLBACK_MAP='/home/zbyszek/src/systemd/src/locale/language-fallback-map' SYSTEMD_KBD_MODEL_MAP='/home/zbyszek/src/systemd/src/locale/kbd-model-map' PATH='/home/zbyszek/src/systemd/build:/home/zbyszek/.local/bin:/usr/lib64/qt-3.3/bin:/usr/share/Modules/bin:/usr/condabin:/usr/lib64/ccache:/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/home/zbyszek/bin:/var/lib/snapd/snap/bin' /home/zbyszek/src/systemd/build/test-boot-timestamps
--- stderr ---
Failed to read $container of PID 1, ignoring: Permission denied
Found container virtualization none.
Failed to get SystemdOptions EFI variable, ignoring: Interrupted system call
Failed to read ACPI FPDT: Permission denied
Failed to read LoaderTimeInitUSec: Interrupted system call
Failed to read EFI loader data: Interrupted system call
Assertion 'q >= 0' failed at src/test/test-boot-timestamps.c:84, function main(). Aborting.

Normally it takes ~0.02s, but here there's a slowdown to 0.73 and things fail with EINTR.
This happens only occasionally, and I haven't been able to capture a strace.

It would be to ignore that case in test-boot-timestamps or always translate
EINTR to -ENODATA. Nevertheless, I think it's better to retry, since this gives
as more resilient behaviour and avoids a transient failure.

See
https://github.com/torvalds/linux/blob/master/fs/efivarfs/file.c#L75
and
bef3efbeb8.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2020-04-24 10:53:46 +02:00 committed by Lennart Poettering
parent 4b6d94a1e5
commit 7229ec02ab
1 changed files with 27 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
src/basic/efivars.c
View File

@ -24,6 +24,10 @@
#if ENABLE_EFI
/* Reads from efivarfs sometimes fail with EINTR. Retry that many times. */
#define EFI_N_RETRIES 5
#define EFI_RETRY_DELAY (50 * USEC_PER_MSEC)
char* efi_variable_path(sd_id128_t vendor, const char *name) {
char *p;
@ -56,8 +60,8 @@ int efi_get_variable(
return -ENOMEM;
if (!ret_value && !ret_size && !ret_attribute) {
/* If caller is not interested in anything, just check if the variable exists and is readable
* to us. */
/* If caller is not interested in anything, just check if the variable exists and is
* readable. */
if (access(p, R_OK) < 0)
return -errno;
@ -66,7 +70,7 @@ int efi_get_variable(
fd = open(p, O_RDONLY|O_NOCTTY|O_CLOEXEC);
if (fd < 0)
return -errno;
return log_debug_errno(errno, "open(\"%s\") failed: %m", p);
if (fstat(fd, &st) < 0)
return -errno;
@ -76,9 +80,26 @@ int efi_get_variable(
return -E2BIG;
if (ret_value || ret_attribute) {
n = read(fd, &a, sizeof(a));
if (n < 0)
return -errno;
/* The kernel ratelimits reads from the efivarfs because EFI is inefficient, and we'll
* occasionally fail with EINTR here. A slowdown is better than a failure for us, so
* retry a few times and eventually fail with -EBUSY.
*
* See https://github.com/torvalds/linux/blob/master/fs/efivarfs/file.c#L75
* and
* https://github.com/torvalds/linux/commit/bef3efbeb897b56867e271cdbc5f8adaacaeb9cd.
*/
for (unsigned try = 0;; try++) {
n = read(fd, &a, sizeof(a));
if (n >= 0)
break;
log_debug_errno(errno, "read from \"%s\" failed: %m", p);
if (errno != EINTR)
return -errno;
if (try >= EFI_N_RETRIES)
return -EBUSY;
usleep(EFI_RETRY_DELAY);
}
if (n != sizeof(a))
return -EIO;
}