Documentation: Improve crash_kexec_post_notifiers description

The crash_kexec_post_notifiers description could be improved a bit,
by clarifying its upsides (yes, there are some!) and be more descriptive
about the downsides, specially mentioning code that enables the option
unconditionally, like Hyper-V[0], PowerPC (fadump)[1] and more recently,
AMD SEV-SNP[2].

[0] Commit a115895 ("x86/Hyper-V: Report crash register data or kmsg before running crash kernel").
[1] Commit 06e629c ("powerpc/fadump: Fix inaccurate CPU state info in vmcore generated with panic").
[2] Commit 8ef9795 ("crypto: ccp: Add panic notifier for SEV/SNP firmware shutdown on kdump").

Reviewed-by: Stephen Brennan <[email protected]>
Signed-off-by: Guilherme G. Piccoli <[email protected]>
Reviewed-by: Michael Kelley <[email protected]>
Signed-off-by: Jonathan Corbet <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: guilhermepiccoli

Documentation/admin-guide/kernel-parameters.txt

@@ -918,12 +918,16 @@
 			the parameter has no effect.
 
 	crash_kexec_post_notifiers
-			Run kdump after running panic-notifiers and dumping
-			kmsg. This only for the users who doubt kdump always
-			succeeds in any situation.
-			Note that this also increases risks of kdump failure,
-			because some panic notifiers can make the crashed
-			kernel more unstable.
+			Only jump to kdump kernel after running the panic
+			notifiers and dumping kmsg. This option increases
+			the risks of a kdump failure, since some panic
+			notifiers can make the crashed kernel more unstable.
+			In configurations where kdump may not be reliable,
+			running the panic notifiers could allow collecting
+			more data on dmesg, like stack traces from other CPUS
+			or extra data dumped by panic_print. Note that some
+			configurations enable this option unconditionally,
+			like Hyper-V, PowerPC (fadump) and AMD SEV-SNP.
 
 	crashkernel=size[KMG][@offset[KMG]]
 			[KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel'