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ANDROID: remoteproc: sysfs: fix race while updating recovery flag

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We have debug features [1] to allow recovery of subsystem or crash
entire system to collect dumps for further analysis based on
recovery flag and when multiple clients (user space or kernel via
android_vh_rproc_recovery_set() vendor hook) try to update
the recovery flag, it is possible that, race condition would
lead to undesired results as updates to recovery flag isn't
protected by any mechanism today. To avoid such issues, take
remoteproc mutex lock before updating recovery flag and release
the lock once done.

Here is the scenario:
====================
1. We have downstream API which can be used by Kernel clients to
update the recovery_disabled flag.

2. Kernel client calls API to set recovery_disabled to false to
recover the subsystem instead of taking down entire system.

3. At around same time user space (via sysfs) tries to set the
recovery_disabled to true to take down entire system.

CPUX                                    CPUY
(update via sysfs)                      (update via Kernel client)
recovery_store()
    |                                   save_restore_recovery()
recovery_disabled = true;                        |
    |                                   recovery_disabled = false;
android_vh_rproc_recovery_set();

At this point, vendor_cb() running on CPUX invoked by vendor hook
which has save/restore functionality for recovery_disabled will
see undesired results.

[1]
https://lore.kernel.org/lkml/20221228162040.m3ucsyau3s55rkfn@builder.lan/T/
https://lore.kernel.org/lkml/20230201054609.14575-1-quic_satyap@quicinc.com/T/

Bug: 266790242
Change-Id: If880122be7f637b4215629117595f6ed7e833cd4
Signed-off-by: Satya Durga Srinivasu Prabhala <quic_satyap@quicinc.com>
This commit is contained in:
Satya Durga Srinivasu Prabhala 2023-01-29 14:36:56 -08:00 committed by Treehugger Robot
parent cc50e0da70
commit e2839b887e
1 changed files with 4 additions and 0 deletions
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4
drivers/remoteproc/remoteproc_sysfs.c
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@ -51,12 +51,16 @@ static ssize_t recovery_store(struct device *dev,
if (sysfs_streq(buf, "enabled")) {
/* change the flag and begin the recovery process if needed */
mutex_lock(&rproc->lock);
rproc->recovery_disabled = false;
trace_android_vh_rproc_recovery_set(rproc);
mutex_unlock(&rproc->lock);
rproc_trigger_recovery(rproc);
} else if (sysfs_streq(buf, "disabled")) {
mutex_lock(&rproc->lock);
rproc->recovery_disabled = true;
trace_android_vh_rproc_recovery_set(rproc);
mutex_unlock(&rproc->lock);
} else if (sysfs_streq(buf, "recover")) {
/* begin the recovery process without changing the flag */
rproc_trigger_recovery(rproc);